Calculating Angle to fire at

[Issues]

Ok I don't know why but I am kind of stumped as how to calculate the angle needed to fire at a targed x meters away that is y meters above the launcher when your robot is capable of firing at v meters per second.
From the kinematic equations
y= -0.5*g*t^2+v*sin(theta)*t
x= v*cos(theta)*t

t=x/(v*cos(theta))

Now I plug that into the first equation which is dandy but then I cant isolate theta... It is rather easy to do when the beginning and ending heights are the same. Maybe I need to brush up on my trig but this is as far as I get
y= (-g*x^2*sec^2(theta))/(2*v^2) + x*tan(theta)

Help would be appreciated