Awoman of 75kg skis down a 50m high hill , the frictional force is not negligible her speed at the bottom of the hill is only 25m\sec, What is the work done by the frictional forces

Awoman of 75kg skis down a 50m high hill , the frictional force is not negligible her speed at the bottom of the hill is only 25m\sec, What is the work done by the frictional forces