There are four test in the semester and each test has equal value. The first three tests had scores of 70, 85, and 75. What score do I need on the final test to get and A for the course?
no idea. What numeric score is equivalent to an A?
Once you figure that out, if you need an average of A, then your final exam score of x must satisfy
70+85+75+x >= 4A
However, I seriously doubt that with the scores shown you have any chance of finishing with an A grade.