For this case, the first thing we must do is define variables.
 m: number of times you cut the grass
 d: amount of dollars you earn.
 We now write the linear equation that models the problem:
 d = 12m
 The slope of the line is 12, which means that each time you cut the grass, you earn 12 dollars.
 Answer:
 an equation for the number of dollars, d, you earn when you mow the lawn m times is:
 d = 12m
