Answer:
12.5
Step-by-step explanation:
4+21=25
25/2=12.5
Answer:

Step-by-step explanation:

Apply formula:
and

We get:







Hence final answer is

She has to buy both binders and notebooks. So, you have to take into account that she has to have both. The closest you can get to $20 while still getting notebooks, is to buy 4 binders. 4 times 4 equals 16. So, she can get 4 binders and 2 notebooks, because then, 2 times 2 equals 4 and 16 plus 4 equals 20.