How would you find the equation if each copy of a book costs 18$ and shipping is 9$ per order

answer:   x = 3 + √11     and     x = 3 - √11

step-by-step explanation:

x² - 6x + 9 = 11

(x - 3)² = 11

x - 3 = ±√11

    x = 3 ± √11

x = 3 + √11     and     x = 3 - √11

what level of math? also i don't need to be paid if i can you.