The process to use here is:
1. calculate the time it takes for the lemming to fall 4.9 meters, using d = (1/2)gt^2. Then the horizontal distance traveled in that time comes from d = v_x t, where v_x is the horizontal velocity,
2. Speed is the magnitude of the vector sum of the horizontal plus vertical components of velocity, v_x + v_y. You already have v_x. V_y can be found from v_y = gt. Use Pythagoras to find the magnitude of their sum.
3. KE = (1/2) mv^2, using the velocity you calculated above.
