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:
[tex]y=50+2x[/tex]Now, using the values of x we want to calculate, we have that:
[tex]\begin{gathered} x=5\colon \\ y=50+2\cdot5=50+10=60 \\ \\ x=10\colon \\ y=50+2\cdot10=50+20=70 \\ \\ x=15\colon \\ y=50+2\cdot15=50+30=80 \end{gathered}[/tex]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:
