Question 1010204
One way to do this is to count the score on the 4 tests, and that is 273.
The average score on those 4 tests is 273/4=68.25
You can now use that 3 times and the final score 1 time to get an average of 70, if that is what a C is.  I am assuming that.
Therefore, 68.25+68.25+68.25+x=280, because 4*70=280.
The first 3 add up to 204.75.
subtract that from 280, and you need a 75.25 on the final.