$40/12 = unit rate simplify = 10/3
$10/3 per book
18 * 10/3 = $60 for 18 copies

Because

is singular, we have

from which it follows that either

or

.
Expression: 3⁴ . 2³
= 3 * 3 * 3 * 3 * 2 * 2 * 2
= 81 * 8
= 648
In short, Your Answer would be: 648
Hope this helps!
Answer:
1.) ???
2.) (2x+3y)(2x-3y)=4x²-9y²