Answer:
A. $657.03
Explanation:
She wants to buy a computer and a monitor. All together, they both cost $871.04+$315.07, or $1185.11. This is how much she needs in order to be able to buy both.
Now, she only has $529.08. In order to find out how much is needed for her to have $1185.11, you need to find the difference between the two numbers. $1185.11-$529.08, or $$657.03. This is how much more she needs to get the computer and monitor.
(Just remember, it's $529.08 + how much more she needs = $871.04 plus $315.07. This can all be simplified to $529.08 + how much more she needs = $1185.11 and now you just solve for the difference, as shown above)