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 20 as well and sum (Inside, Outside) to equal -9. For this problem, those two numbers are -5 and -4. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 9y + 20
y² + (-5 - 4)y + (-5 x -4)
(y - 5)(y - 4)

The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(9²) + 2π(9 x 1)
sa = 2π(81) + 2π(9)
sa = (2 x 81)π + (2 x 9)π
sa = 162π + 18π
sa = 180π

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

a² + 6a + 8 = 0
(a + 2)(a + 4) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (a + 2) or (a + 4) must equal zero:

If (a + 2) = 0, a must equal -2
If (a + 4) = 0, a must equal -4

So the solution is that a = -2 or -4

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

a = l x w
a = a x b
a = 4 x 1
a = 4

The formula for circumference is circle diameter x π. Circle diameter is 2 x radius:

c = πd
c = π(2 * r)
c = π(2 * 6)
c = 12π