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 1 x 9) + (2 x 9 x 7) + (2 x 1 x 7)
sa = (18) + (126) + (14)
sa = 158

The area of a trapezoid is one-half the sum of the lengths of the parallel sides multiplied by the height:

a = ½(b + d)(h)
a = ½(3 + 7)(3)
a = ½(10)(3)
a = ½(30) = \( \frac{30}{2} \)
a = 15

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.

8a⁴ - 4a⁴ = 4a⁴

To solve this equation, 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.)

-8b(b - y)
-8(-3)(-3 - 6)
-8(-3)(-9)
(24)(-9)
-216

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.

9a - 3a = 6a