Rational number word problem: cab

sandy is taking a cab in New York City the taxi fare includes a base charge of $2 50 as soon as you enter the cab plus an additional 250 per mile traveled if sandy starts off with a $20 bill takes the cab for five miles and leaves a $1 tip how much money will she be left with well let's first just think about how long how much this five mile cab ride is going to cost her so the cost so cab cab I'll call it the cab fare cab fare so it's going to be two dollars 50 just when you get into the cab plus $2 50 per mile plus $2 50 per mile well she's going to go for five miles five miles times $2 fifty two dollars right this way times two dollars fifty two dollars fifty per per mile so the cab fare here is just going to be two dollar fifty two dollar fifty this to our 50 plus five times 250 let's see five times 250 that is $12 and fifty $12 $12.50 250 plus $12.50 is going to be $15 so just the cab fare is going to be $15 and then sandy gives a one dollar tip so fair fair plus tip is going to be equal to the cab fare $15 plus $1 which is equal to $16 so then answering the question how much money would she be left with with a $20 bill well we could write her change is going to be she's going to give a $20 bill the fare is the fare plus tip is $16 plus minus 16 so she's going to have $4 left in change