The area of a book cover is 63.8 in². the width of the book is the difference of the length and 3 inches. let x represent the book's length. which quadratic equation represents the area of the book cover?
x(x - 3) = 63.8
x(3 - x) = 63.8
2x - 3 = 63.8
x + x - 3 = 63.8

In this item, we are already given that the length of the rectangular book can be represented by the variable x. In this way, the width, which was described to be the difference of the length and 3 inches, can be expressed as x - 3. 

The area of the triangle is rectangle is calculated by multiplying the length, x, and the width, which was derived to be x - 3.

                 Area = Length x width
                 Area = (x)( x - 3)

Putting in the value of the area, we have the final answer as,
               x(x - 3) = 63.8 in²

Hence, the final answer is the first answer.