Question 312625
30% sulphuric acid  = 70% water
15% sulphuric acid = 85% water

Let quantity of water be x ml
concentration equation 
x+0.7*10 = 0.85(x+10)
x+7=0.85x+8.5
0.15x=1.5
x= 1.5/0.15
x=10 ml