Two casks of 48 and 42 liters are filled with mixture of wine and water13 : 7 and 18 : 17. If the contents of the two casks be mixed and 20 liters of water added to the whole what will be the proportion of wine to water in the result?

• 13 : 12
• 12 : 13
• 21 : 31
• 31 : 21