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

a = l x w
a = a x b
a = 6 x 8
a = 48

The formula for circumference is circle diameter x π:

c = πd
c = 9π

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 7 as well and sum (Inside, Outside) to equal -8. For this problem, those two numbers are -7 and -1. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 8y + 7
y² + (-7 - 1)y + (-7 x -1)
(y - 7)(y - 1)

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.

9a - 9a = 0a

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.)

-2b(b - y)
-2(-6)(-6 - 4)
-2(-6)(-10)
(12)(-10)
-120