the question Im having a hard time dealing with is this equation

y"(t)=-g where g is the gravity at 9.8m/s^2

and the boundaries are

y(0)=0.9144 and y(3)=0

how to solve this problem? I am having trouble with runge kutta since it is only a constant function? what to do pls?

I need to know how many shots to and the graph. thanks