I'm assuming no air friction here, first use conservation of energy to find velocity, so initially all the energy is from the spring, (1/2)kx^2, then it is converted to kinetic energy, (1/2)mv^2. so .5kx^2=.5mv^2. the .5s cancel, kx^2=mv^2. solve for v, v=sqrt(kx^2/m) plug in your values for the variables and find v. then use vf^2=vi^2+2ax in the u direction and solve for vf, vf=sqrt(vi^2+2ax). use that velocity in vf=vi+at and solve for t. vi=0 and a=g=9.81, so vf/a=t. plug in the values from the previous equation and the acceleration due to gravity to find the time it takes to hit the ground vertically. Now use v=x/t and solve for x. x=vt, plug in the velocity of the ball horizontally, which we found with the conservation of energy part, and y which we found with the previous equation, and you get your x, the distance it will take for the ball to hit the ground.
