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.

4a + 6a = 10a

The coordinate grid is composed of a horizontal x-axis and a vertical y-axis. The center of the grid, where the x-axis and y-axis meet, is called the origin.

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 4 x 7) + (2 x 7 x 1) + (2 x 4 x 1)
sa = (56) + (14) + (8)
sa = 78

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

y² + 6y - 27 = 0
(y - 3)(y + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (y - 3) or (y + 9) must equal zero:

If (y - 3) = 0, y must equal 3
If (y + 9) = 0, y must equal -9

So the solution is that y = 3 or -9

The formula for area is πr²:

a = πr²
a = π(4²)
a = 16π