The largest side (b) pf a triangle is nine more units than the smallest side (a). The third side (c) is twice the smallest side. The shortest side is x cm. If the perimeter is 25 cm wirte and solve an equation to find the lengths of all three sides

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%)