There are in total 1200 references,
No. of hits in L1 : 1200-60 = 1140, so L2 will be referenced 60 times out of which 30 are misses in L2
No. of hits in L2 : 60-30, so MM will be referenced 30 times.
Access time for 1200 references:1140*acesstime(L1) + 60* acesstime(L2+L1) + 30*acesstime(MM+L2+L1)
Average access time: 1140*acesstime(L1) + 60* acesstime(L2+L1) + 30*acesstime(MM+L2+L1) / 1200
(OR)
L1 will be referenced 1200 times, (hit + miss)
L2 will be referenced 60 times, (hit + miss)
MM will be referenced 30 times, (hit)
Access time for 1200 references: 1200*acesstime(L1) + 60*acesstime(L2) + 30*acesstime(MM)
Average access time: 1200*acesstime(L1) + 60*acesstime(L2) + 30*acesstime(MM) / 1200