A single-phase $100$ kVA, $1000$ V / $100$ V, $50$ Hz transformer has a voltage has a voltage drop of $5 \%$ across its series impedance at full load. Of this, $3\%$ is due to resistance. The percentage regulation of the transformer at full load with $0.8$ lagging power factor is
1. $4.8$
2. $6.8$
3. $8.8$
4. $10.8$