The first thing we are going to do is convert 5 years to months. We know that there are 12 month in a year, so we just need to multiply 5 by 12 to get the number of months in 5 year:

Now we just need to divide the total projected savings ($15000) by the number of months in 5 years (60):
Minimum savings per month:
We can conclude that the minimum monthly deposit the family should make is they want to save $15000 in 5 years is $250