A gardener plans to extend the length of a rectangular garden by 7 feet. Let x represent the​ garden's original length. The expression 9(x+7) represents the area of the​ garden, where 9 is the​ width, in​ feet, and (x+7) represents the extended​ length, in​ feet, of the garden. When asked for the area of the extended​ portion, the gardener incorrectly said it was 16 square feet. Expand the expression to find the area of the extension.

To expand the expression, we can distribute the 9 to both terms inside the parentheses:

9(x + 7) = 9x + 63.

So, the expression 9(x + 7) represents the area of the garden, which is 9x + 63 square feet.

To find the area of the extension, we can subtract the original area from the extended area:

Area of extended portion = (9x + 63) - x = 8x + 63 square feet.

Therefore, the area of the extension is 8x + 63 square feet.