A quadrilateral is a shape with four sides. The perimeter of a quadrilateral is the sum of the lengths of its four sides.

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 18 as well and sum (Inside, Outside) to equal 9. For this problem, those two numbers are 3 and 6. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 9y + 18
y² + (3 + 6)y + (3 x 6)
(y + 3)(y + 6)

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 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 + 2a = 7a

To solve this equation, 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.)

-7c(c - x)
-7(-7)(-7 - 2)
-7(-7)(-9)
(49)(-9)
-441