First, you need to find out how many zippers are used to make one bookbag. To do that, you divide the zippers used to make the 3 backpacks.
12 / 3 = 4
So, 4 zippers are used per bookbag. Then, you divide the number of available zippers by four to find out how many bags she can make.
48 / 4 = 12
Roberta can make 12 bookbags.
