When solving an equation with two variables, 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.)

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

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

sa = 2πr² + 2πrh
sa = 2π(2²) + 2π(2 x 2)
sa = 2π(4) + 2π(4)
sa = (2 x 4)π + (2 x 4)π
sa = 8π + 8π
sa = 16π

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 solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

-7b + 9 = \( \frac{b}{-8} \)
-8 x (-7b + 9) = b
(-8 x -7b) + (-8 x 9) = b
56b - 72 = b
56b - 72 - b = 0
56b - b = 72
55b = 72
b = \( \frac{72}{55} \)
b = 1\(\frac{17}{55}\)