The correct option is D 6
As the 7th term exceeds the 5th term by 12, so the 5th term will exceed the 3rd term by 12 as well
So, n3=16
n5=28
n7=40
n4 or n6 can be calculated by taking average of the preceding and next term
So, n4=(28+16)/2=22
This gives the d=6
AP:4,10,16,22,28,34,40,46,.......