Let consider, the TLB hit ratio is p.
TLB access time =100 ns
page table Access time =600 ns
now in the question they asked the time for virtual address translation.
virtual address translation time = check in the TLB for the mapping + if not found in TLB then check in page table .
now,
virtual address translation time = TLB hit ratio * TLB access time + (1- TLB hit ratio)(TLB access time + memory access time to accesss the page table)
virtual address translation time =p*100 +(1-p)(100+500) [ assuming single level page table]
100p+600-600p=200
or,500p=400
p=0.8
So, TLB hit ratio is 0.8.