What is the distance acted by the kinetic friction in a slipping ball until it starts rolling?

Initially at time t=0, a solid sphere slides with velocity v along a horizontal surface. The coefficient of friction is u. Find the required time for the sphere to stop sliding (the sphere will then be rolling).

I decided to solve it using energy methods. I assumed that the work done by the friction force would be $$-F_{f} d$$ where $$d$$ is the displacement from $$x_{0}$$ to the point where the ball starts rolling without slipping.

Some people pointed me out that the distance the kinetic friction force acts is not really the displacement, $$d$$. But the translational distance $$x$$, minus the total rotational arc done by the ball, $$s$$, up to the point of rolling.

$$d = x - s$$

However, I don't fully understand what do they mean by that.