Question

What is the equation I should use?

Answer 1

start by drawing a diagram

now you have an idea of what you need to do.

You will need pythagoras' theorem and solve for h

\[h^2 + 15^2 = (h + 4)^2\]

only consider the positive answer... as measurements can't be negative.

Hope it helps

Answer 2

isn't the 15 squared and (h+4) squared be reversed

Answer 3

well reading the question, the shorter sides of the triangle are the base of 15 ft and height of the tree (h)

so the wire is the hypotenuse

seems the sensible way to approach the question