9.5 For the following ideal systems, calculate the speedup ratio S. In each case, tc is the access time of the cache memory, tm is the access time of the main store, and h is the hit ratio.
a. tm = 70 ns, tc = 7 ns, h = 0.9
b. tm = 60 ns, tc = 3 ns, h = 0.9
c. tm = 60 ns, tc = 3 ns, h = 0.8
d. tm = 60 ns, tc = 3 ns, h = 0.97