A transformer has a primary coil of 400 turns and a secondary coil of two hundred turns. If the primary coil is connected to 240 AC mains, calculate the efficiency given that the current in the primary coil is \(3 \mathrm{~A}\) and in the secondary \(5 \mathrm{~A}\).
A. \(60 \%\) B. \(50 \%\) C. \(83 \%\) D. \(62.5 \%\)