Equations with several variables (letters) are called
literal
equations.
Your job, usually, will be to solve the equation for one of the variables.
The letters that do not represent your desired variable move to the other side of the equal sign so that the one variable you are solving for stands
alone.
Even though there are more letters
in these equations, the methods used to solve these equations are the
same as the methods you use to solve all equations.
Example #1 
Steps 
Solve for x: 

ax + b = c
 b b

1. Move
b
(the opposite of add is
subtract) 
ax = c  b

2. Move
a
(the opposite of
multiply is divide) 

3.
x is what we are solving for and it stands alone.
Done.

Example #2 
Steps 
Solve for h: 

A
= ½ b h

1. Move
b by
division 

2.
Move the ½ by multiplying by the
reciprocal (2/1) 

3.
h is what we are solving for and it stands alone.
Done.

Application
Problem 
Shoe sizes and foot length are
related by the formula
S = 3F  24,
where S
represents the shoe size
and F represents the length
of the foot, in inches.
Solve the formula for
F. 
Solution:

Steps: 
S = 3F
 24

add 24 to both
sides 
S +
24 = 3F

divide both
sides by 3 

simplify 

Done.

