Guys how do you find out a average of some numbers?

For how answer my question this will be the last question can you answer in math subject

Plz ( true - false) all triangles have interior angles whose measure sum to 90.

Question 1 of 10 2 points different groups of 50 graduates of an engineering school were asked the starting annual salary for their first engineering job after graduation, and the sampling variability was low. if the average salary of one of the groups was $65,000, which of these is least likely to be the average salary of another of the groups? o a. $64,000 o b. $65,000 o c. $67,000 o d. $54,000