In 40 litres mixture of milk and water the ratio of milk to water is 7 : 1. In order to make the ratio of milk and water 3 : 1, the quantity of water (in litres) that should be added to the mixture will be

• A. 6
• B. <table><tr><td rowspan="2">6</td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td></tr><tr><td style="text-align: center;">2</td></tr></table>
• C. <table><tr><td rowspan="2">6</td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>2</center></td></tr><tr><td style="text-align: center;">3</td></tr></table>
• D. <table><tr><td rowspan="2">6</td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>3</center></td></tr><tr><td style="text-align: center;">4</td></tr></table>