The answer is B because you are takin away $50 a week. $200 is what she wants to have at the end off the summer. So that automaticly means it is ≥ 200. She is TAKING AWAY $50 a week. Meaning - 50w ≥ 200. Finally she has $800 to begin with. So, 800 - 50w ≥ 200.
Sorry if l am not very well at explaining this kind of stuff. Let me know if you need anymore help!!