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 - 6)(y + 5)
(y x y) + (y x 5) + (-6 x y) + (-6 x 5)
y² + 5y - 6y - 30
y² - y - 30

The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

b² - b - 72 = 0
(b + 8)(b - 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (b + 8) or (b - 9) must equal zero:

If (b + 8) = 0, b must equal -8
If (b - 9) = 0, b must equal 9

So the solution is that b = -8 or 9

The formula for circumference is circle diameter x π:

c = πd
c = 14π

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.

3a⁴ - 5a⁴ = -2a⁴

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.

(7a)(3ab) + (7a²)(4b)
(7 x 3)(a x a x b) + (7 x 4)(a² x b)
(21)(a¹⁺¹ x b) + (28)(a²b)
21a²b + 28a²b
49a²b