An equation is two expressions separated by an equal sign. The key to solving equations is to repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

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 -42 as well and sum (Inside, Outside) to equal 1. For this problem, those two numbers are -6 and 7. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + y - 42
y² + (-6 + 7)y + (-6 x 7)
(y - 6)(y + 7)

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.

(3a)(5ab) - (8a²)(4b)
(3 x 5)(a x a x b) - (8 x 4)(a² x b)
(15)(a¹⁺¹ x b) - (32)(a²b)
15a²b - 32a²b
-17a²b

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 6 x 5) + (2 x 5 x 7) + (2 x 6 x 7)
sa = (60) + (70) + (84)
sa = 214

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.