Final answer:
The area of the book cover can be found by multiplying the length and width.
Step-by-step explanation:
To find the area of the book cover, we need to multiply the length and width of the cover.
The length of the book cover is (x + 6) inches and the width is (-3) inches.
Using the distributive property, the area of the book cover is (x + 6)(-3), which simplifies to -3x - 18 square inches.
Therefore, the correct answer is option a) Area = (x + 6)(-3) square inches.