Asquare garden has an area of 1600 feet length of each side

* L is the Length and A is the Area

L * L = A
L * L = 1600
L^2 = 1600
√L^2 = √1600
L = 40 feet

The length of each side is 40 feet.

Btw: this was your question "A square garden has an area of 1600 feet length of each side"

When it should be . . .

"A square garden has an area of 1600 feet squared length of each side"

tan y° because r is opposite side and p is adjacent side