Ok, I need some help getting started with a problem involving a spring and projectile motion. A picture of the problem is attached. Part A was easy, done with projectile motion. I worked it out to time = sqrt((-2h)/g). Now I'm stuck on where to start with part B because we are not given a spring constant. I know that just the speed as it leaves the platform needs to be found because there is no acceleration on the x component. I played around with simple harmonic motion equations but keep getting stuck on the fact that I dont know what K is or the force needed. And for reference I'm in ap physics b. Any help to get me started would be greatly appreciated. Thanks.