For a particular heat engine, 3,000 J of energy goes in at 700 K and 2000 J comes out at 200 K. The rest of the energy is used work.

What is the actual efficiency of this engine?

Amount of heat goes in the engine $Q_H = 3000$ J

Amount of heat rejected by the engine $Q_R = 2000$ J

Thus work done by the engine $W = Q_H - Q_R =3000 - 2000 = 1000$ J

Actual efficiency of heat engine $\eta = \dfrac{W}{Q_H} = \dfrac{1000}{3000} = 0.33$