Assume a is the longer side and b is the shorter side
2a + 2b = 112cm
b=3/4a
if we substitue the value for b into the top equation we would get 2a + 3/4a + 3/4a = 112
Solve for 7/2a = 112
A = 32
Then substitute A back into b = 3/4a
b= 3/4(32)
b= 24
To make sure this is correct we can add the 4 sides. 32 + 32 + 24 + 24 should equal the perimeter of 112 which they do.