Answer:
13 weeks.
Step-by-step explanation:
First, you want to take out the numbers stated in the question. In this case, you would take out the information that he needs $520 for the bike, $65 to pay his sister back, and he is able to save $45 once a week.
Next, you want to add $520 and $65, so you know how much money in total he needs to save.
Lastly, once you get your total you want to divide that by his weekly pay which leaves you with 13 weeks to save up to buy a bike and pay his sister back.