Question 144660
It looks like you intended for {{{x}}} to represent the length of the diagonal.  If that is the case, and the diagonal is 3.6 feet longer than the length of the rectangle, then the length of the rectangle has to be 3.6 feet SHORTER than the diagonal.  Hence, the length of the rectangle would be represented by {{{x - 3.6}}}.  Similarly, the width of the rectangle would be {{{x - 7.1}}}.  Since the diagonal is the hypotenuse of a right triangle, and the width and length of the rectangle are the legs of that triangle:


{{{x^2=(x-3.6)^2+(x-7.1)^2}}}


Now expand that and solve the quadratic to get your dimensions.


By the way, since your given dimensions are expressed to the nearest 1/10 of a foot, your answer should not be expressed to any greater precision.