In 250 litres mixture of soda and water the ratio of amount of soda to that of water is 7 : 18. In order to make this ratio 2 : 3, how many more litres of soda should be added?
A man travelled a distance of 61 km. in 9 hours , partly by walking at speed of 4 km / hr and partly on bicycle at speed of 9 km / hr. The distance covered by walking is