Let A be the 15% canned juice and B be 5% juice
Va + Vb = 10
Vb = 10 - Va
Concentration of final solution = 12% juice
10 x 0.12 = Va x 0.15 + Vb x 0.05
Substituting Vb from the first equation:
1.2 = 0.15Va + 0.5 - 0.05Va
Va = 7 liters
Vb = 3 liters
7 liters of the 15% juice and 3 liters of the 5% juice.
