A 4.0x10^4 kg roller coaster starts from rest at point A. Neglecting friction, calculate its potential energy relative to the ground, its kenetic energy, and its speed at points B, C, and D

i found the potential energy of all points, i just need to know how to calculate the speed first, because i need speed to calculate kinetic energy

we know that acceleration due to gravity is 9.81 m/s ^2

point B is at the bottom of a slope which is 15m above the ground and the mass of the roller coaster is 4.0 x 10^4 kg heavy, how would i calculate the speed of the roller coaster at this point?

any help would be greatly appreciated!