The eighth-grade class at Lincoln Middle School has $$93$$ students. Each student takes a maths class or a foreign language class or both. There are $$70$$ eighth-graders taking a maths class, and there are $$54$$ eighth-graders taking a foreign language class. How many eighth graders take only a maths class and not a foreign language class? 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle->Inclusion-Exclusion Principle for Two Sets