What is the square footage of....?

Question

I have an irregular shape (for a treehouse) between trees. It measures 11' * 13' * 18' * 15'

I need to know the square footage. Please include the math.

Answer 1

You need the measure of the angle between corresponding sides. There are an infinite number of possible areas with the given four lengths.

Answer 2

without knowing more about the shape - like if the corners are square, etc - it's impossible to say.