Rational number word problem: school report

Joell is working on a school report in a word processor processor she wants to place a figure which is thirteen point zero nine centimeters wide so that it appears centered on the page the width of the page is twenty-one point five nine centimeters how much margin should she leave on the left so that the figure is centered so let's visualize what's going on we have a page that's twenty-one point five nine centimeters wide so this distance right over here is twenty-one point five nine centimeters so this right over here that is our page let me draw the actual page we'd rather than white since paper tends to be white so this is her page our page is twenty-one point five nine centimeters wide it's just like that's a little unusual dimension for a piece of paper but we'll go with it and then she wants to place a figure that is thirteen point zero nine centimeters wide in the center of the page so the figure the figure I'll do in magenta the field like that's not magenta the figure is thirteen point zero nine centimeters so let's say that this is the figure right over here so this is the figure that she wants to place in the middle of the page so this is thirteen point zero nine centimeters zero nine centimeters so the question is how much margin should she leave on the left so that the figure is centered so they're really asking what how much what should this distance what should this distance be here so that the figure is centered and the key thing is if the figure is centered this distance is going to be the same as this distance so that the figure is right in the middle whatever this is is going to be the same as this so one way we could think about it we could say ok let's take thirteen point zero nine centimeters from twenty-one point five nine centimeters and if we do that then we'll be left over what will well know how much leftover space this Plus this combined is and then we just want to split that space in half we want half of it to go on the right side and we want half of it to go on the left side so let's see how much this left margin and right margin combined need to be and that's just 21 point five nine that's just going to be twenty-one point five nine centimeters - - thirteen point zero nine centimeters and this we get to let's see this is this is 8.50 centimeters which is the combined margins not just the left or not just the right this is the left plus the right margin is 8.50 centimeters this is this distance Plus this distance now if we want to figure out what the left margin should be if we want to Center it well we just want to split this evenly between the left and the right margin so we just want to divide this by two so if you divide eighteen point five oh by 2 or multiply it by 1/2 I guess that might be a little bit more obvious either way so if we multiply this by 1/2 you are left with half of 8.50 is 4.25 centimeters so if we want it centered this is going to be four point two two five centimeters and of course this is going to be four point two five centimeters as well and you see when you add four point two five to four point two five you get eight point five centimeters and then you add that to thirteen point zero nine you get the entire width of the piece of paper so how much margin should she leave on the left four point two five centimeters