Final answer:
The function rule for the area of a rectangle whose length is 6 ft more than its width is A = w(w + 6). When the width is 12 ft, the area of the rectangle is 216 square feet.
Step-by-step explanation:
To write a function rule for the area, A, of a rectangle whose length is 6 ft more than its width, we can use the formula A = w(w + 6). When the width is 12 ft, plug in the value of w into the formula: A = 12(12 + 6) = 12(18) = 216 square feet. So, the area of the rectangle is 216 square feet when its width is 12 ft.