How do you evaluate variable expression ?

Hint: We just have to substitute the given values in the given equation. Questions similar in nature can be approached in a similar manner and we can solve it easily. It is the type of question where only mathematical operations such as addition, subtraction, multiplication and division is used.

Complete step by step solution:
Let us suppose we have two variables in our expression.
There are many methods by which you can solve the equations with two variables. Here we have discussed two simple methods that are ,
1. Substitution method
 we have to write one equation in terms of one variable, and then substitute that value in the second equation.
2. Elimination method
a. Firstly, multiply one or both the equations such that so that they have the same coefficients.
b. Then, add or subtract one equation from another equation.
c. then substitute that value in the second equation.
Example: How do you evaluate \[13 - 0.75w + 8x\] when \[w = 12\] and \[x = 1/2\] .
We have \[13 - 0.75w + 8x\] where \[w = 12\] and \[x = 1/2\]
We just have to substitute the given values of w and x in the given equation ,
We will get the following result,
 \[13 - 0.75w + 8x\]
 \[ = 13 - 0.75(12) + 8\left( {\dfrac{1}{2}} \right)\]
 \[
   = 13 - 9 + 4 \\
   = 4 + 4 \\
   = 8 \;
 \]
Hence we get the result.

Note: If we know the values of the variables present in the expression , we just have to replace the variables with their corresponding values and then evaluate the given expression. There are many methods by which you can solve the equations with two variables. We just have to substitute the given values in the given equation.