Check Out At The Check In/Walkthrough

One must go to Escobar International to the payphone inside and pick up the phone. First, one must get the sniper rifle that he left for you at the drop point behind the tree behind you. Then, you find the woman that's indicated and follow her with your scope. When she goes up to a man and asks the time, there's your target. When indicated, you should kill that man and take the briefcase he drops. Run outside, get a fast car, and then drive to the Ammu-Nation in Downtown (Vice City), and when you get there and step inside, the mission is complete. Be very careful and very fast, because you will be followed by a few black Admirals with men shooting Uzis at you; they can very easily pop your tires, so get away from them as soon as you can.

You can also use a helicopter to get away. Which is less risky. (Leave your weapons behind they'll still be there when you go back.) Remember, it takes 6 seconds to take off with a helicopter so if cops get near you get out and kill them.