TLB hit: 0.96 → This Means we have LA with us.
TLB miss: 0.04 → We now look for LA in 2-level PT.
Cache-hit: 0.90 → Respective frame found.
Cache-miss: 0.10 → Now try to find the page frame in MM
MM access time: 10ns
Cache access time: 1ns
TLB access time: 1ns
0.96 * [1 + 0.9*(1) + 0.10*(1+10) ] + 0.04 * [1 + 2*10 + 0.9*(1) + 0.10*(1+10) ] = 3.5 ≈ 4 (answer)
If you understand these below lines then, I think this question is over for you.
TLB → hit : now we have LA, check the cache for respective frame : → hit : 1ns
→ miss : 1ns + 10ns (checking MM)
→ miss : check 2-level PT & get LA, now check the cache for respective frame : → hit : 1ns
→ miss : 1ns + 10ns (checking MM)