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

sa = 2πr² + 2πrh
sa = 2π(4²) + 2π(4 x 2)
sa = 2π(16) + 2π(8)
sa = (2 x 16)π + (2 x 8)π
sa = 32π + 16π
sa = 48π

When solving an equation with two variables, 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.)

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 x 3b = (5 x 3) (a x b) = 15ab

To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses:

(y - 1)(y + 8)
(y x y) + (y x 8) + (-1 x y) + (-1 x 8)
y² + 8y - y - 8
y² + 7y - 8

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.

5a⁵ + 5a⁵ = 10a⁵