On the first 3 tests of his geometry class, Daniel got an average score of 79. What does he need on the next test to have an overall average

Getting an average of 79 on three tests is the same as getting a 79 on each test.

So after four tests, he will have the same score as    79 + 79 + 79 + x

The average of these four scores can be found by:  (79 + 79 + 79 + x) / 4

Since this average is 82, use the equation:             (79 + 79 + 79 + x) / 4  =  82

Simplify:                                  (237 + x) / 4  =  82

Multiply both sides by 4:                  237 + x  =  328

Subtract 237 from both sides:                    x  =  91