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.)

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

a = l x w
a = a x b
a = 7 x 3
a = 21

A line on the coordinate grid can be defined by a slope-intercept equation: y = mx + b. For a given value of x, the value of y can be determined given the slope (m) and y-intercept (b) of the line. The slope of a line is change in y over change in x, \({\Delta y \over \Delta x}\), and the y-intercept is the y-coordinate where the line crosses the vertical y-axis.

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 - 4)(y + 2)
(y x y) + (y x 2) + (-4 x y) + (-4 x 2)
y² + 2y - 4y - 8
y² - 2y - 8

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 5 as well and sum (Inside, Outside) to equal 6. For this problem, those two numbers are 1 and 5. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 6y + 5
y² + (1 + 5)y + (1 x 5)
(y + 1)(y + 5)