A Man, A Ladder And A Pulley

Let us say that the rope moves some distance $x$ when the man climbs. So the net displacement of the man is $15-x$ . The ladder, whose mass is $60-40=20$ kg moves a distance $x$ in the downward direction, thus it's net displacement is $-x$ .

The counter weight moves a distance $x$ in the upward direction. Hence the displacement of the centre of mass would be:

$\begin{aligned} \Delta \vec r_{\text{cm}}&=\dfrac{40(15-x)+20(-x)+60(x)}{40+20+60}\\ &=\dfrac{40\times 15}{120}\\ &=\boxed 5 \end{aligned}$