Inductors in series
As long as magnetic fields around inductors do not interact, inductances in the series add like resistances in series. The total value is the sum of the individual values. It is important to be sure that you are using same size units for all inductors when you add their values.
Problem:
Three 40-µH inductors are joining in series, and there is no interaction, or mutual inductances, between them . What is the total inductance?
You can just include up the values. Call the inductances of the individual elements L1, L2, and L3, and the total inductance L. Then L = L1+ L2 + L3 = 40+ 40 + 40 + 120µH.