How do you do this problem and how do you get the answer?

What it means for two things to be proportional is that one thing affects the other. So, this question is asking if the amount of profit eiither affects or is affected by the number of belts sold. This of course is true because as the number of belts sold increases, the profit does as well. So, the amount of profit is directly proportional to the number of belts sold!

Yes i also think it is b