Hi Codyh,
we are given the that angle 1 + angle 2 =180 ==> supplementary
and also angle 3+angle 4 =180 ====> also supplementary
since angle 1 is congruent to angle 4
then angle 3+angle 1 =180
but angle 2+angle 1 = 180 as well
it must be then angle 2 is congruent to angle 3
