The first thing to do is to calculate the total energy in the system, which the problem kindly provides us with.
We assume that there is no air resistance or friction so that the conservation of energy holds true. Therefore, the total energy 3.01 x 10^5 will be constant.
At point C, there is a gravitational potential energy U and a kinetic energy K. We calculate U using U=mgh=(1500)(9.8)(16)=235200J. Subtracting this from the total energy, we see that the rest of the energy is 65800J, all of which is kinetic energy. Then, we use K=(1/2)mv^2 => 65800=(1/2)(1500)v^2, seeing that v=sqrt(65800/((1/2)(1500)))=9.367m/s.
At point D, you will perform the same calculations except U=(1500)(9.8)(10)=147000J and K=154000J=(1/2)(1500)v^2, getting v=sqrt(154000/((1/2)(1500)))=14.329m/s.