The volume of a cube is height x length x width:

v = h x l x w
v = 2 x 1 x 3
v = 6

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.

5a⁷ + 7a⁷ = 12a⁷

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 35 as well and sum (Inside, Outside) to equal 12. For this problem, those two numbers are 5 and 7. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 12y + 35
y² + (5 + 7)y + (5 x 7)
(y + 5)(y + 7)

The surface area of a cube is (2 x length x width) + (2 x width x height) + (2 x length x height):

sa = 2lw + 2wh + 2lh
sa = (2 x 9 x 4) + (2 x 4 x 1) + (2 x 9 x 1)
sa = (72) + (8) + (18)
sa = 98

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².