A rectangle has a side length of 4 inches and an area of 18 square inches and a larger similar triangle has a corresponding side length of 8 inches. Find the area of the larger triangle.

I have to assume that you mean it is a similar rectangle, since a triangle can not be similar to a rectangle. In that case the original measurements are 4x4.5.

By doubling them, you get a rectangle with the measurements of 8x9 and thus the area is 72