104,976 square feet you do 324 x 324, because its 324 to the 2 power.
Remark
Make up a proportion that relates the tree and its properties to the stick and its properties.
Givens
Stick height (s_h) = 4
Stick shadow(s_s) = 2
Tree shadow = t_s = 18
Tree height = x
Formula
s_h / s_s = x / t_s
Substitute and solve.
4/2 = x / 18 Cross multiply
4*18 = 2 * x
72 = 2x Divide by 2
72/2 = x
x = 36
The height of the tree is 36 feet.
Simplified, it"s y=-3/2x+22.5
Divide 3 on both sides
x=3.33
