Answer:
77 units^2
Explanation:
I'm going to call the red square A, green square B, blue square C.
A side of a square is the square root of the area.
The Pythagorean Theorem is A^2 + B^2 =C^2.
So in other words,
33 + 44 = the side of square C^2.
33+44=77
One side of square C is √77.
Square this to get the area.
Square C's area is 77 units^2.