Explanation:
as they are scaled copies of each other, it means that there is one and the same scale factor for all the sides and their counter parts.
so, let's look for a pair of sides, where we have both sizes.
we find that with the bottom sides : 4 and 10.
since we need to go from 25 to x, we check the factor to get from 10 to 4.
10 × f = 4
f = 4/10 = 2/5 = 0.4
for the other direction (from small to large) that would be then 1/(2/5) = 1/1/2/5 = 5×1/(2×1) = 5/2 = 2.5
so,
25 × f = x
25 × 0.4 = x
x = 25 × 4/10 = 100/10 = 10
Part A :
depending on the direction the scale factor f is
f = 2.5 (from small to large)
f = 0.4 (from large to small)
Part B :
x = 10