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.

(2a)(6ab) - (7a²)(9b)
(2 x 6)(a x a x b) - (7 x 9)(a² x b)
(12)(a¹⁺¹ x b) - (63)(a²b)
12a²b - 63a²b
-51a²b

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

9a⁹ - 2a⁹ = 7a⁹

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

-4b - 3 = 7 - 9b
-4b = 7 - 9b + 3
-4b + 9b = 7 + 3
5b = 10
b = \( \frac{10}{5} \)
b = 2

The surface area of a cube is (2 x length x width) + (2 x width x height) + (2 x length x height):

sa = 2lw + 2wh + 2lh
sa = (2 x 3 x 5) + (2 x 5 x 5) + (2 x 3 x 5)
sa = (30) + (50) + (30)
sa = 110

The formula for area is πr². Radius is circle \( \frac{diameter}{2} \):

r = \( \frac{d}{2} \)
r = \( \frac{10}{2} \)
r = 5
a = πr²
a = π(5²)
a = 25π