Answer:

Step-by-step explanation:
Given:
The equations given are:

Now, a linear function is of the form:

Where, 'm' and 'b' are real numbers and 
Equation 1: 
Simplifying using distributive property, we get:

The above equation is of the form
. So, it represents a linear function.
Equation 2: 
Here, both sides of the equation has same variable 'X'. So, it will form an equation of 1 variable. So, it's not a linear function.
Equation 3: 
Simplifying the above equation. This gives,

This is not of the form of the linear function. So, it is also not a linear function.
Equation 4: 
Simplifying the above equation. This gives,

This is not of the form of the linear function. So, it is also not a linear function.