Inelastic Human Cannonball

Question:

Thank you for your help! I have another problem for you. I will probably have a few more before Monday if you don't mind, because I'm having a test over this material. I have also forwarded your site to other classmates like myself who have been out of school for 20+ years, and need a little extra help.

Here is the problem:
In a circus act, Marcello (mass 70kg) is shot from a cannon with a muzzle velocity of 24.00 m/s at an angle of 30 degrees above the horizontal. His partner, Tina (mass 50kg), stands on an elevated platform located at the top of his trajectory. He grabs her as he flies by and the two fly off together. They land in a net at the same elevation as the cannon a horizontal distance x away. Find x.

The text gives a partial solution to this one. However, I cannot figure out how to get the final velocity, unless it is equated somehow with the initial velocity.
Vxi = (24cos30) m/s = (70*20.8)kgm/s = (120* Vxf)kgm/s;
Vxf = 12.1 m/s
time of flight to the platform: t = (24 sin 30)/gs = 1.22s
x = (20.8 + 12.1)1.22m = 40.1 m

The part I do not understand, is how to find the final velocity.