The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(9²) + 2π(9 x 9)
sa = 2π(81) + 2π(81)
sa = (2 x 81)π + (2 x 81)π
sa = 162π + 162π
sa = 324π

The formula for circumference is circle diameter x π. Circle diameter is 2 x radius:

c = πd
c = π(2 * r)
c = π(2 * 11)
c = 22π

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.

(4a)(7ab) - (9a²)(2b)
(4 x 7)(a x a x b) - (9 x 2)(a² x b)
(28)(a¹⁺¹ x b) - (18)(a²b)
28a²b - 18a²b
10a²b

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.

(5a)(9ab) + (2a²)(5b)
(5 x 9)(a x a x b) + (2 x 5)(a² x b)
(45)(a¹⁺¹ x b) + (10)(a²b)
45a²b + 10a²b
55a²b

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 < sign and the answer on the other.

8b + 6 < -3 - 5b
8b < -3 - 5b - 6
8b + 5b < -3 - 6
13b < -9
b < \( \frac{-9}{13} \)
b < -\(\frac{9}{13}\)