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.

5a - 9a = -4a

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.

7a³ + 4a³ = 11a³

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 5 x 8) + (2 x 8 x 9) + (2 x 5 x 9)
sa = (80) + (144) + (90)
sa = 314

A parallelogram is a quadrilateral with two sets of parallel sides. Opposite sides (a = c, b = d) and angles (red = red, blue = blue) are equal. The area of a parallelogram is base x height and the perimeter is the sum of the lengths of all sides (a + b + c + d).

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.

(7a)(3ab) + (5a²)(5b)
(7 x 3)(a x a x b) + (5 x 5)(a² x b)
(21)(a¹⁺¹ x b) + (25)(a²b)
21a²b + 25a²b
46a²b