Please view the screenshot below

b = 363

Step-by-step explanation:

Sum of a geometric Progression is expressed as attached.

a = 3 = the first term

r = 3 = the common ratio

n = 5 = number of term

Sum of GP = a(r^n - 1)/ r-1

= 3(3^5 - 1)/ 3-1

= 3(234 - 1) / 2

= 3(242) / 2

= 726/2

= 363

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.