PLEASE HELP! Carla and Jonah are working together to determine if quadrilateral CDEF with coordinates C(2, 3), D(1, 2), E(4, 1), and F(5, 3) has a right angle.

Carla sets up the following equations:
the slope of segment CD equals 2 minus 3 all over 1 minus 2
the slope of segment DE equals 1 minus 2 all over 4 minus 1

Jonah sets up the following equations:
the slope of segment CD equals 2 minus 3 all over 1 minus 2
the slope of segment EF equals 3 minus 1 all over 5 minus 4

Who is on track to get the correct answer and why?