Let's say
P = perimeter, L : Length and w : width
Then

But

So


We verify :
Length = L = 38Width = w = 16
a square has four equal sides, and we know the perimeter or namely the sum of all those four sides is 1/7 yard, so
s = length of one side.

The index of radical expression is the number indicating which root (square root, cube root, etc.) is meant.
If there's no index on the radical expression, then it's assumed to be square root.
I think so C is correct
Because is true.