What is the difference of the polynomials? (–2x3y2 + 4x2y3 – 3xy4) – (6x4y – 5x2y3 – y5)

–6x4y – 2x3y2 + 9x2y3 – 3xy4 + y5
–6x4y – 2x3y2 – x2y3 – 3xy4 – y5
–6x4y + 3x3y2 + 4x2y3 – 3xy4 + y5
–6x4y – 7x3y2 + 4x2y3 – 3xy4 – y5

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%)