From a cask filled with 867 litres of wine, y litres are first drawn and replaced with water. After the first replacement the ratio of wine and water in the cask, when expressed in the lowest form, is given as a :
b. From this mixture y litres are drawn and replaced with water. The ratio of wine to water in the cask after the second replacement, when expressed in the lowest form, is given as 169 : 120. Find the value of (y + a +
b).