math
posted by Jennifer .
Jane is taking a class and asks you to help her figure out what her last grade must be in the class to get a 85 in the class. She tells you the following calculation is used to find your final grade:
75+85+90+X
 > or = to 85
4
x is her last score which has not been taken. Explain this equation and the process you would use to solve for the unknown test score. Solve for the test score.
Can you please explain the process you used to solve? Thank you

75+85+90+x/4=85
250+x/4=85
250+x= 340
x=90