The calculate the current drawn by the prime of a transformer which steps down $200\;v$ to $20\;v$ to operate a device of resistance $20 \Omega$ the efficiency of the transformer to be $80\%$

Question

$\begin{array}{1 1} 0.125\;A \\ 1.25\;A \\ 12.50\;A \\ 125\;'A \end{array}$