As we know that in transformers we have
[tex]\frac{V_s}{V_p} = \frac{N_s}{N_p}[/tex]
here we know that
[tex]V_s = 4 Volts[/tex]
[tex]V_p = 120 Volts[/tex]
[tex]N_s = 50 coils[/tex]
[tex]N_p = 300 coils[/tex]
now from above equation we will have
[tex]\frac{V}{120} = \frac{50}{300}[/tex]
[tex]V = 20 Volts[/tex]
now we have to reduce this voltage to final voltage of V = 4 V
so again we will have
[tex]\frac{V_s}{V_p} = \frac{N_s}{N_p}[/tex]
[tex]\frac{4}{20} = \frac{N_s}{N_p}[/tex]
[tex]\frac{N_s}{N_p} = \frac{1}{5}[/tex]
so we need to take such a winding whose ratio is 1:5
So it is satisfied in X
[tex]N_p = 60[/tex]
[tex]N_s = 12[/tex]
so answer will be
B)- X