Why is it difficult to make a fusion reaction occur? ?

Because in order for fusion to occur high temps are needed to cause the reaction. In nuclear fusion weapons a nuclear fission reaction takes place first to provide the raw energy needed to even make the fusion reaction occur.

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.