The area of a parallelogram is equal to its length x width:

a = l x w
a = a x b
a = 8 x 1
a = 8

Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other. Same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°).

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)(8b)
(2 x 6)(a x a x b) + (7 x 8)(a² x b)
(12)(a¹⁺¹ x b) + (56)(a²b)
12a²b + 56a²b
68a²b

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 9) + (2 x 9 x 4) + (2 x 3 x 4)
sa = (54) + (72) + (24)
sa = 150

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.

4a - 7a = -3a