exam Maths Puzzle Numerical Ability

Suppose y varies directly as x and that y=21 when x=3. Find the value of y when x=5.

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A teacher bases her class grade on four exams @100 pts. each. George has taken 3 exams with an average grade of 87%. What does he need on his fourth exam, to give him a final grade of 90%?
I have no idea. Please help!! Identify whether the parabola y=-(x-3)^2 +6 opens up or down and identify the vertex, x-intercepts and y-intercepts. I know it opens down but, I am not sure how to identify the intercepts or vertex (3,6)?