An equation is two expressions separated by an equal sign. The key to solving equations is to repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 2 + 1 + 4 + 8
p = 15

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

9a + x = 8
x = 8 - 9a

then substitute the result (8 - 9a) into the second equation:

4a + 9(8 - 9a) = -9
4a + (9 x 8) + (9 x -9a) = -9
4a + 72 - 81a = -9
4a - 81a = -9 - 72
-77a = -81
a = \( \frac{-81}{-77} \)
a = 1\(\frac{4}{77}\)

To solve this equation, isolate the variable for which you are solving (c) on one side of the equation and put everything else on the other side.

8c - z = -5c - 5z + 8
8c = -5c - 5z + 8 + z
8c + 5c = -5z + 8 + z
13c = -4z + 8
c = \( \frac{-4z + 8}{13} \)
c = \( \frac{-4z}{13} \) + \( \frac{8}{13} \)
c = -\(\frac{4}{13}\)z + \(\frac{8}{13}\)

The volume of a cylinder is πr²h:

v = πr²h
v = π(6² x 2)
v = 72π