I m not sure but I think it could be 77?
1) 3 2)10 3)30 4)47 5)?
Between 1 and 3 there is a difference of 27( 3+27=30)
Between 2 and 4 there is a difference of 37(10+37=47)
Between 3 and 5 it could be a difference of 47 (30+47=77)
