A cooling system that pumps 177,21 kg/s of water in a tunnel warmed by trains with an average thermal output of 37,125 mega watts. I have to estimate the energy which is necessary to run the system in order to cool down water with the mass M. Both in the general case and on the assumption that the new water temperature is nearly the same. I have never made an estimation in physics before. Do I have to calculate? Is there a difference between both cases? Normally the formula for thermal power is p=(m*c*dT)/t. Can I apply it? Thank you for your support.