For this one it's really simple. Just do 90-(-2). It may look confusing right now, but it's really easy. All you need to know is that a negative and a negative cancel out to form a positive. So it's actually 90+2. 92 is the difference.
Well I don't know if i'm answering the question, but 30 workers surveyed were satisfied with the benefits they received from the employers because 300 multiplied by .10 is 30. Hope my answer is useful.