You have to divide 300 with 15, the answer to that is: 300/15=20. However, if she starts saving this week (counting as a first), she will have enough money in 19 weeks after the first week, she needs 20 weeks to save the money.
By either writing and solving a simple equation (15w=300) or dividing by 15, you can figure out how many amounts of 15 would need to be saved to get 300.
