To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(9a)(6ab) - (8a²)(9b)
(9 x 6)(a x a x b) - (8 x 9)(a² x b)
(54)(a¹⁺¹ x b) - (72)(a²b)
54a²b - 72a²b
-18a²b

The formula for area is πr²:

a = πr²
a = π(5²)
a = 25π

To solve this equation, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

-9b(b - x)
-9(-4)(-4 - 4)
-9(-4)(-8)
(36)(-8)
-288

A trapezoid is a quadrilateral with one set of parallel sides.

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce -18 as well and sum (Inside, Outside) to equal 3. For this problem, those two numbers are -3 and 6. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 3y - 18
y² + (-3 + 6)y + (-3 x 6)
(y - 3)(y + 6)