Charles is saving $5 each week. he earns an extra $15 by mowing his neighbors lawn. how many weeks does he need to save in order to get $75

Hey there!!

Given amount of information:

With this given information, we get to know that the number 15 is a constant and we don't know the number of weeks. Hence, it is a variable.

Let's take the number of weeks as 'w'

Let's now form a equation.

... 5w + 15 = ?

The total amount we want is $75. Hence,

... 5w + 15 = 75

... 5w + 15 - 15 = 75 - 15

... 5w = 60

... 5w/5 = 60/5

... w = 12

Hence, the number of weeks is 12.