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.)

To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses:

(y - 8)(y - 5)
(y x y) + (y x -5) + (-8 x y) + (-8 x -5)
y² - 5y - 8y + 40
y² - 13y + 40

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.

9a³ + 2a³ = 11a³

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 2 + 7 + 4 + 6
p = 19

You need to find the value of c so solve the first equation in terms of z:

-7c + z = -4
z = -4 + 7c

then substitute the result (-4 - -7c) into the second equation:

3c + 6(-4 + 7c) = 7
3c + (6 x -4) + (6 x 7c) = 7
3c - 24 + 42c = 7
3c + 42c = 7 + 24
45c = 31
c = \( \frac{31}{45} \)
c = \(\frac{31}{45}\)