Question: Physic problem

I had the worst physic's teacher in High School so we did not learn a single thing. If you guys could help me I'd appreciate! I need to find the angle if A throws a rock at C. He throws his rock at 20m/s. C is on a 8metres building. A is 10metres away from C. With which angle (theta) A needs to throw his rock to hit C. Situation: http://img522.imageshack.us/my.php?image=problemkk3.jpg Equation: http://img519.imageshack.us/my.php?image=physicequationpa1.jpg
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