Since the triangles are similar, the ratio of each side in one triangle to
the corresponding side in the other one is always the same number.
We know what one pair of sides is ... 3.5 and 7 ... so we know that
each side in the first triangle is 1/2 as long as the corresponding side
in the other one.
So we can say with assurance that ...
y = 1/2 (x + 4)
and
x = 1/2 (3y) .
That's all the intelligence required for this problem. The rest is just algebra,
and I should not need to go through all the routine misery for you here.
When you solve this pair of equations slowly, carefully, and accurately,
you'll find that the sides of the triangles are ...
3.5, 8, 12
and
7, 16, 24 .
