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.

6a⁷ + 3a⁷ = 9a⁷

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.)

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 5 x 4) + (2 x 4 x 8) + (2 x 5 x 8)
sa = (40) + (64) + (80)
sa = 184

You need to find the value of a so solve the first equation in terms of x:

3a + x = 1
x = 1 - 3a

then substitute the result (1 - 3a) into the second equation:

-9a - 2(1 - 3a) = -1
-9a + (-2 x 1) + (-2 x -3a) = -1
-9a - 2 + 6a = -1
-9a + 6a = -1 + 2
-3a = 1
a = \( \frac{1}{-3} \)
a = -\(\frac{1}{3}\)

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.