Answer:
Let x represent the amount of weeks she is saving up for the bike, and y represents the cost of the bike.
The equation would look like this:
So, let's say the bike costs $2000.
Divide 2000 by 20, and it will give you the x value (or, the amount of weeks it will take)
It will take 100 weeks for her to save $2000 for the bike, if she puts back $20 each week.