May and Nancy have equal number of pieces of ribbon. They each have a mix of long and short ribbons. The length of each piece of short ribbon is $40\textasciitilde cm$ and each piece of long ribbon is $70\textasciitilde cm$. May has $7$ pieces of short ribbon and Nancy has $18$ pieces of long ribbon. The total length of May\textquotesingle s ribbons was $2.4\textasciitilde m$ longer than the total length of Nancy\textquotesingle s ribbons. How many pieces of ribbon does May have? 
Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle