20. Let I represent an execution of init(s), W of wait(s), and S of signal(s). Then, for example, IWWS represents the sequence of calls init(s), wait(s), wait(s), and signal(s) by some processes in an operating system. For each of the following sequences of calls, state the value of s and the number of processes blocked after the last call in the sequence:

*

(a) IW

(b) IS

(c) ISSSW

(d) IWWWS

(e) ISWWWW