The rule of the area of a rectangle is

W is the width
H is the height
Since the ratio between width and height is 9: 6 and the height is 36 inches, then we will use the ratio method

By using the cross multiplication

Divide both sides by 6

Then the width of the rectangle is 54 inches
Substitute W by 54 and H by 36 in the rule of the area to find it

The area of the rectangle is 1944 square inches