Answer:
For finding the inflection points you'll have to put the first derivative equal to zero and solve for x. After you've done that, you can plug in the x you've just found into the original function and find also the y, so you'll find the ordered pair (x,y) of the inflection point(s).
The function represents the profit, and the company obviously wants to maximize it.
You can see that the profit increases until the parabola reaches its maximum.
The coordinate of the maximum look like (1.5, 90)
This means that, if the company invests 1.5 thousand dollars, the profit will be 90 thousand dollars, and this is the maximum profit the company can reach.
From the equation of motion, we know,

Where s= displacement
u= initial velocity
a= gravitational force
t= time
Displacement is 0 since the ball comes back to the same point from where it was thrown.
A =
since the ball is thrown upwards.
Plug the known values into the equation.
=> 
Solving for u gives :
u= 16.67 m/ sec ....... equation (1)
At maximum height, final velocity i.e v is 0
Time take to reach the top = 

=> 
Solving for s we get
s= 14.16 m