This can be solved using Inclusion–exclusion principle (IEP). Let us denote the sets of books covering each language as J, P, and C. The set of all books is , though these three sets intersect invarious ways. By IEP,
You know the left-hand side and all but the last term in the right-hand side, so you can find the last one.
Next, Let be the set of books about Python only. Then . Again we have the union of three sets. Apply IEP to this union. This will allow you to find .
It may also help looking at the three-set diagram on the Wikipedia page given above.