A square window would have 4 equal sides
so 126 / 4 =31.5
Meaning each side othe square window would cost $31.50.
Then I see that it is a trick quetion as that has nothing to do with the question at all.
So to the equation C= 3.5 n^2
C=126
126 = 3.5 n^2
dived both sides by 3.5
126 / 3.5 = 36 3.5(n^2) / 3.5 = (n^2)
36 = n^2
Take the square root of both sides
(6*6) = 36 (n*n)=(n^2)
6=n
n=6
Length of each side is 6 feet.