Lets take a example
no of instruction =6
i=4(Normal instrction execution time)
j=2(Additional time incase of page fault)
k=3(Page fault occurs on every kth instruction)
Total time required=4+4+(4+2)+4+4+(4+2)=28
Average time=28/6=4.66
Now substitute the i,j,k values in options
i+j/k=4+2/4=4.66
so A is the answer