TLB lookup time = $20$ ns
TLB hit ratio = $80$%
Memory access time = $75$ ns
Swap page time = $500,000$ ns
$50%$ of pages are dirty
Page Fault rate =$10$%
When there is a TLB hit, we no need to consider page fault,moreover here is no requirement of page translation. Because that information not given in question.
When TLB miss is occured then only we need to check, if there is a page fault or not
if there is a page fault, we need to consider, page fault service time
So,
TLB hit(TLB access time)+TLB miss(no pagefault*MM access time+pagefault(dirty page*PFST+no dirty page*2*PFST))
=$0.8(20+75)+0.2[0.9(20+75+75)+0.1(0.5\times 500000+0.5(2\times 500000))]$
=$0.8\times 95+0.2[153+0.1(250000+ 500000))]$
=15106.6ns