The combinations P and S are series combinations. Hence, the effective inductance cannot be 1H. This leaves combinations R and Q. For combination R, L1+L2=5H
‌‌
1
L1+L2
+‌
L
L3
=‌
1
5
+‌
1
6
=‌
6+5
30
=‌
11
30
‌∴‌‌L‌eff ‌=‌
30
11
=2.72H ∴‌‌ The correct combination would be Q.