Is there no solution, one solution or many solutions for 21+2.5w=6+5.7w-3.2w+15?

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Which equation is y = -6x2 + 3x + 2 rewritten in vertex form?

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%)