Question 1169635
Let x = the number of liters of the 10% solution. Then 10-x is the volume of the 
30% solution.
The final mixture is 10 liters, of which 15% is acid.
So the final mixture has 0.15*10 = 1.5 liters of acid
1.5 = 0.1x + 0.3(10-x) -> 1.5 = 0.2x -> x = 7.5 liters