If Jonathan has $18 and wants to buy oranges at the rate of 12 oranges for $4, you can calculate how many oranges he can buy by dividing his money by the cost of 12 oranges:
$18 ÷ $4 = 4.5
Jonathan can buy 4.5 sets of 12 oranges. However, since you can't buy a fraction of an orange, he can buy a total of 4 sets of 12 oranges.
So, Jonathan can buy 4 sets of 12 oranges, which is a total of 48 oranges.