Speed of cricket ball after 20m with air drag

[bennyq]

Homework Statement

At international cricket games, it is commonplace to display on the scoreboard a speed for each bowl. Because the ball is subject to a drag force due to air proportional to the square of its speed given by R = kmv^2, it slows as it travels 20 m toward the wicket according to the formula v = vie^(−kx). Suppose the ball leaves the bowler's hand at 151 km/h. Ignore its vertical acceleration, and determine the speed of the ball when it hits the wicket. (For a cricket ball, assume the mass is 0.16 kg, the radius is 3.5 cm, and the terminal velocity is 40 m/s. The density of air is 1.2 kg/m3.)

Homework Equations

Apart from the equations i have tried R=0.5DpAv^2
but i don't know the drag coefficient!

The Attempt at a Solution

Honestly i don't know where to start, i have tried googling a similar question also.
The problem is I cannot figure out R. If i knew drag coefficient i could work out k, then work out v over the distance

 

[AlephZero]

What is the drag force at the termimal velocity? You can work out "k" using that information.

 

[bennyq]

I worked drag force R out with R = -bV and using the above formal for R with a drag coefficient of .3 which i found online. Both gave a similar result. I got 133km/h