Normal Distribution and Standard Deviation

This is the question:

Hermione runs a coaching college and gives all her students an exam at the end of the course. from past experience she knows that the results are normally distributed with a mean of 76.5% and standard deviation of 7.5%. the latest course has 2000 students and hermione offers to refund the cost of the course to any student who does not score a certain percentage.

what should this percentage be if hermione is only prepared to refund 3 students?

justify your answer with calculations and include at least ONE diagram in your solution.

kk.. well ive got an answer with not much working and wonder if there is any more and i cannot find a diagram to use. can someone please help??