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.

7a - 3a = 4a

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

z² + 11z + 28 = 0
(z + 4)(z + 7) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (z + 4) or (z + 7) must equal zero:

If (z + 4) = 0, z must equal -4
If (z + 7) = 0, z must equal -7

So the solution is that z = -4 or -7

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 - 7)(y + 4)
(y x y) + (y x 4) + (-7 x y) + (-7 x 4)
y² + 4y - 7y - 28
y² - 3y - 28

A rectangle is a parallelogram containing four right angles. Opposite sides (a = c, b = d) are equal and the perimeter is the sum of the lengths of all sides (a + b + c + d) or, comonly, 2 x length x width. The area of a rectangle is length x width. A square is a rectangle with four equal length sides. The perimeter of a square is 4 x length of one side (4s) and the area is the length of one side squared (s²).

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

sa = 2πr² + 2πrh
sa = 2π(3²) + 2π(3 x 4)
sa = 2π(9) + 2π(12)
sa = (2 x 9)π + (2 x 12)π
sa = 18π + 24π
sa = 42π