Consider a single-phase three-winding transformer with the primary excited winding of N 1 N 1 turns carrying

Consider a single-phase three-winding transformer with the primary excited winding of $N_1$ turns carrying a current $I_1$ and two secondary windings of $N_2$ and $N_3$ turns, delivering currents of $I_2$ and $I_3$ respectively. For an ideal case, how are the ampere-turns balanced?

(a) $N_1{I}_1=N_2{I}_2-N_3{I}_3$

(b) $N_1{I}_1=N_2{I}_2+N_3{I}_3$

(c) $N_1{I}_1=-(N_2{I}_2-N_3{I}_3)$