Since we’re calculating the area of a rectangular garden, we need the rectangular area formula. This formula is A = L*W, where L is the length and W is the width. The width is defined to be 15 feet in the problem, but the length is unknown.
The length is 8 feet more than twice its width. In equation form, this looks like L = 2*W + 8. If we plug in the value for the width, then the length is L = 2*W + 8 = 2*15 + 8 = 38 feet. With the length, we can now calculate the area:
A = L*W = (38 ft)(15 ft) = 570 sq. ft.
The area of the garden is 570 square feet.
Hope this helps!