Answer:
You need to save approximately $28 per week.
Explanation:
1 month = 4 weeks
18 months =

Now we are given that you wanted to save 2000 to buy used car 18 months from now
So,you wanted to save 2000 in 18 months (=72 weeks)
Amount you need to save in 72 weeks = 2000
Amount you need to save in 1 week=

=

So, you need to save approximately $28 per week.