Projectile Motion (cannonball)

A cannonball is fired with an initial speed of 90.0 m/s at an angle 61.0 ° above the horizontal (see diagram). The cannonball strikes point A on top of a cliff 10.0 s seconds after being fired. Ignore air resistance in this problem.

**Calculate the speed of the cannonball just before it hits A.**

http://img24.imageshack.us/img24/6196/cannonball.jpg

My Attempt:

The things I have calculated previously are:

**·** Point A is 436 meters horizontally from the cannon.

**·** The maximum height the cannonball reaches is 316.

**·** The cliff is 297 m high.

Now in order to calculate the speed of the ball before it hits the A, I tried to use the formula $\displaystyle v=v_i + at = 90 + (- 9.81)8.7$ but I do not end up with the correct answer (which is **47.7**). I heard that this formula only works for finding the vertical component of the speed of the cannonball. So what do I need to do??

I even tried using $\displaystyle v=v_i + at$ to find the vertical speed and **v=xt** for the horizontal speed and then add up the two speeds to find the resultant. But this didn't work either... :(