The missing side length seems to be the diagonal side of figure B. I'm not sure what's going on with the vertical side 89.4 as that should be 3 instead (since 1.5*2 = 3).
The diagonal side is 5 units long since we double 2.5 to get 5.
B) Length of left side is 3 and length of right side is 5.
Step-by-step explanation:
A) Length of the top side is 2.5 in A and is 5 in polygon B. 5/2.5 = 2, therefore scale factor is 2.
B) Because the scale factor is 2, each of the sides double while the angles stay the same. Therefore, the length of the side on the left is 3 and length of the side on the right is 5.