Ineed because this question confused me

D. (8,6) is not the answer as it would make it congruent

C. (8,0) also makes it equal, so it's not your answer

B. (5,6) also makes it congruent

A. (4,0) Makes the triangle misshaped and it does not allow it to be a right triangle, so it is not congruent. 
A is your answer

The complete triangle given has a height of 3 and a base of three - that means that the triangle Paula has to match it with has to have the same height and base. The base is already given: S = (5,3) & T = (8,3)
the triangle does not have to match the other one 100% - meaning, you can flip it the other direction(left) or upside-down
A - no number are on 4 so the triangle would be slanting
B - (5,6) matches - just flips to the left
C - (8,0) flips upside-down
D - (8,6) matches triangle RQP