Answer: if 3 for every 1000 students quit due serious health issues, then you can see the proportion doing the quotient between this numbers. This is:
3/1000 = 0.003
Then if you choose a random student, you have a 0.003 probability of choosing one who can have a health issue.
and a 0.997 probability to choose a student with no health issues.
Now, the company wins $50 for the healthy students, and lose ($50 - $8000) = -$7950 for each student that is sick (because they initially pay the 50$ and latter get the $8000).
Then the insurance company should expect to make in average:
0.997*$50 - 0.003*($7950) = $26
So the company should expect to make 26 dollars per student in a year.