The torque about the axis should be the force, T, of the Tension in the rope multiplied by the radius, r, of the pulley.

If you do a free body diagram of the 50kg body you have the force, T, pulling up on the body and the weight of the body which is either 50kg*9.81m/s^2 or 50N they are equivalent.

T = mg

T = 50N

The radius, r, of the pulley is either .15m or 15cm they are also equivalent.

So the torque, J, is equal to 50N * .15m or,

J = 7.5 Nm