Will mark brainliest answer, please answer !!

9 + x

Step-by-step explanation:

The area of a rectangle is length times width.

A = lw

We know the area is 81 - x^2 and the width is 9 - x, so plug them in.

81 - x^2 = 9-x * w

81 - x^2 is a difference of squares in the form a^2 - b^2 = (a-b)(a+b), so we know the width must be 9 + x.

Test it to be sure:

(9 + x)(9 - x)

81 + 9x - 9x -x^2 = 81 - x^2

It works!

step-by-step explanation:

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8 2/3 is the answer

step-by-step explanation: just use a calculator