There are 10 boys and 20 girls in a class they have a test
the mean mark is 60
the mean mark for the girls are 54

mean for the boys?

When the ball hit the ground, the height of the ball will be zero. So using the value of h(x) as zero in the given equation, we can find the time in which the ball will hit the ground.

0 = -(x-2)^2 + 16

(x-2)^2 = 16

x-2 = 16

x-2 = 4

x = 6

This means the ball will hit the ground 6 seconds after Amir threw it.