To find the mean of something, add all the numbers then divide by the number of numbers there are.
40,000 + 50,000 + 40,000 + 60,000 + 90,000 = 280,000
Then divide:
280,000/5 = 56,000
The mean of the annual salaries at the company is 56,000
Hope this helped! If you have anymore questions or don't understand, please comment or DM me. :)