Hi Neha

There cannot be a unique solution to this one if there are not any other conditions attached.

See if I take 100x, 100y and 100z of the three solutions and mix them, then total quantity of mixture becomes 100(x + y + z) quantity and equating the quantity of sloute in the mixture, we get:

40x + 60y + 90z = 67x + 67y + 67z

=> 23z = 17x + 7y

Now this equation has many solutions, that's why I said no unique solution is possible unless some other restrictions are put.