How to create a function?

Question

A rectangle has area 36 m2.

Express the perimeter of the rectangle as a function of the length (L) of one of its sides.

Answer 1

A=36m^2

A= L*W

36=L*W

W=36/L

P=2W+2L

P=2*(36/L)+ 2L= 72/L + 2L = (72+2L^2)/L