First, we need to know how much money Rainn has left after buying the backpack. So, to calculate this quantity, we subtract $7.99 from $20, as:
$20 - $7.99 = $12.01
Now, she has $12.01 for spiral notebooks. So, to calculate how many notebooks can Rainn buy we need to divide $12.01 into $0.79 as:
Therefore, she can buy 15 notebooks
Answer: 15 notebooks