Answer:
There should be 10 l of 25% orange juice and 5 l of 10% orange juice.
Step-by-step explanation:
Let the amount of the 25% orange juice be "x", while the amount of the 10% one be "y". The sum of these must be equal to 15 l, therefore:

The sum of the concentration of juice on each can must be equal to the final product, therefore:

We can now solve the system of equations as shown below:

There should be 10 l of 25% orange juice and 5 l of 10% orange juice.