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.

7a + 9a = 16a

You can only add or subtract monomials that have the same variable and the same exponent. For example, 2a + 4a = 6a and 4a² - a² = 3a² but 2a + 4b and 7a - 3b cannot be combined. However, you can multiply and divide monomials with unlike terms. For example, 2a x 6b = 12ab.

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

sa = 2πr² + 2πrh
sa = 2π(4²) + 2π(4 x 6)
sa = 2π(16) + 2π(24)
sa = (2 x 16)π + (2 x 24)π
sa = 32π + 48π
sa = 80π

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 32 as well and sum (Inside, Outside) to equal 12. For this problem, those two numbers are 4 and 8. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 12y + 32
y² + (4 + 8)y + (4 x 8)
(y + 4)(y + 8)

A monomial contains one term, a binomial contains two terms, and a polynomial contains more than two terms.