Let's have an example of a seller that sells phones.
His salary have a fixed part of $50, and it increases by $2 by each phone he sells.
We want to find out how much will be his salary if he sells 5, 10 and 15 phones.
If we use the variable x to represent the number of phones sold, his salary (variable y) will be defined by the equation:
Now, using the values of x we want to calculate, we have that:
We can plot these points to see how much his salary increases for each phone sold, and also we can have an idea of any point we want to find out: