4. Three enhancements with speedups of 3, 5 and 2, respectively, are considered for a new architecture. Only one enhancement may be active at a time.

(a) If enhancements 1 and 2 are each active for 30% of executed instructions, for what fraction of executed instructions must enhancement 3 be active in order to achieve an overall speedup of 2?

(b) Assume the distribution of enhancement usage is 30%, 30% and 20% for enhancements 1, 2 and 3, respectively. Assuming all three enhancements are incorporated into the architecture, for what fraction of the reduced execution time is no enhancement in use?

(c) Assume that, for some benchmark, the fraction of use (i.e., instructions executed) is 20% for enhancements 1 and 2, and 50% for 3. We want to maximise performance. If only one enhancement can be implemented, which one should it be? If two, which pair should be chosen?