Please help me! Please show work and explain!

I’m stuck on this equation, anyone got the answer?

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%)

If the line in the graph is shifted up two units which is the equation of the new line