Concept:Each term is obtained by adding a number that doubles the previous addition.Explanation:First difference: 9 - 4 = 5.Second difference: 19 - 9 = 10.Third difference: 39 - 19 = 20.Each difference is twice the previous difference. Next difference = 20 × 2 = 40.Missing term = 39 + 40 = 79.
