physics question (answer is given but idk how to get to these answers)

Question

A sled with two riders have a combined mass of 150.0 kg. They slide down a 12.0 m high hill and then across a frozen lake that is 60.0 m in diameter. The frictional force is a constant 200.0 N for the entire length of the run (both down the slope and then across the frozen lake).

a. Find the speed of the sled at the bottom of the hill. [8.67 m/s]

Answer 1

The initial energy = 150*g*12 due to the 12m hill. 200*d of that energy is lost due to friction traveling to the bottom of the hill where d is the sliding distance to the bottom. The remaining energy of .5(150g)v² is used up sliding the 60 meters * 200 N across the lake where v is the velocity at the bottom of the hill. So, 60*200=.5*150gv² yielding v= 4.039 m/s (regardless of the answer you were given)