If the ratio of the number of bottles of apple juice to the number of bottles of orange juice was 3:2, then you can denote 3x - the number of bottles of apple juice and 2x - the number of bottles of orange juice.
After he sold 64 bottles of apple juice, the number of bottles of apple juice became 3x-64 and the number of bottles of orange juice remained 2x.
The new ratio is 1:6, this means that

Solve this equation:

In the end Mr. Young had:
bottles of apple juce;
bottles of orange juice.