Each of the six surfaces of the box is a rectangle (if square, a square is a rectangle...). Find the area of each of the surfaces using length X width, then add the six areas together. That's the total surface area of the box.

Actually, they're in pairs of two - opposite surfaces are the same. So you could find the three surfaces and multiply by 2.

Actually, they're in pairs of two - opposite surfaces are the same. So you could find the three surfaces and multiply by 2.