Write an equation of the line represented by the table below. Table:
x | f(x)
0 | 6
2 | 2
4 | -2
6 | -6

Astudent must have an average on five test that is greater than it equal to 80% but less than 90% to receive a final grade of b. devon's greades on the first four test were 78% 62% 91% and 80% what range if grades on the fifth test would give him a b in the course? ( assuming the highest grade is 100%)