You need to calculate the work output of the machine. The efficiency is simply the ratio of work output over work input.

Work = Force x distance.

However, there is not enough information provided to calculate the force. If the object is being lifted then the force is 9.81 x 600. If the object is being dragged across a horizontal surface then the force is dependent on a coefficient of friction. There are many other possibilities, the object could be dragged up a hill or through a viscous fluid.