Answer:
6
Step-by-step explanation:
Sum of first 4 numbers= 4*5= 20
This includes 3 + 4th number
Sum of last 4 numbers= 4*8= 32
This includes 4th number + 3
Sum of 7 numbers= 7*(6+4/7)= 46
This includes 3+4th number +3
Number common to both sets= (20+32)- 46 = 6