Please please help me with this question just help me on (C)

Answer:
move 3 seconds on your x-axis, and find your intersection with you y axis to determine the height h in m.
Am assuming you drew the function...
substitute 3 in the equation
[tex]h=-5({t})^{2} +20t\\ h=-5({3})^{2} +20(3)\\h=60-45=15m[/tex]