Quadrilateral problems on the coordinate plane

Problem

Rectangle A, B, C, D is graphed in the coordinate plane. The following are the vertices of the rectangle: A, left parenthesis, 2, comma, 1, right parenthesis, B, left parenthesis, 5, comma, 1, right parenthesis, C, left parenthesis, 5, comma, 6, right parenthesis, and D, left parenthesis, 2, comma, 6, right parenthesis.
Given these coordinates, what is the length of side A, B of this rectangle?
  • Your answer should be
  • an integer, like 6
  • an exact decimal, like 0, point, 75
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
units