let c be the time required to check whether corresponding frame no to the page is in TLB .
If a page is present in TLB(hit) then Effective Memory Access time(EMAT)= c+m ( c to visit TLB and m to visit the memory using the frame no(that we got using TLB) and offset)
If a page is not present in TLB then EMAT=c+2m ( here additional m because if the page is not in TLB then you have to visit page table to get frame no so additional m )
Assume hit ratio is x ,
so EMAT= x(c+m) + (1-x)(c+2m)
given x=70% and c=30ns and m=90ns
so, EMAT= (0.7)(30+90) + (0.3)(30+2*90)
EMAT=147ns