homework and exercises - Calculating angle of projectile motion

I realize that similar questions have been asked but I'd like to put my problem here and what I have to make sure everything is right.

So my problem is: I've got a rock $2.5$ meters above the ground and I shoot it out of a slingshot. It hits another rock which is $3.6$ meters above the ground, $14$ meters away from it's initial position $x$. The initial velocity of the rock is $15.9$ m/s.

So the formula I know is: $\frac{1}{2} \cdot g \cdot t^2 - (v_o \cdot \sin ( \theta ) ) + y$

I also know: $x = (v_o \cdot \cos ( \theta ) ) \cdot t$

But these don't seem to help me solve my problem as I don't have $t$ nor $\theta$.