Acollege student purchase 10 posters for her dorm room but she only has space to hang six of them how many specific ways can student arrange and hang these six posters on her wall

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%)