Can you explain this exercise solution to me?
According to this article: F. J. Corbató, M. M. Daggett, R. C. Daley, An Experimental Time-Sharing System (IFIPS 1962), CTSS uses a "multi-level scheduling algorithm":


  The basis of the multi-level scheduling algorithm is to assign each user program as it enters the system to be run (or completes a response to a user) to an $\text{ell}$-th level priority queue. The process starts with the time-sharing supervisor operating the program at the head of the lowest level occupied queue, $\text{ell}$, for up to $2^\text{ell}$ quanta of time and then if the program is not completed (i.e. has not made a response to the user) placing it at the end of the $\text{ell}+1$ level queue. Programs are initially entered into a level $\text{ell} = 0$.


A program at the ell-th level is assigned $2^{\text{ell}}$ quanta.

Now you know how to solve your exercise.