Harry had a painting that he wanted to turn into lego of the same proportion. The ratio of the length and the breadth of the painting is $5:2$. Given that the length of the painting is $90\textasciitilde cm$ and the length of the lego has to be $70.5\textasciitilde cm$ smaller, determine the maximum size of the breadth of the lego. 
Overseas Competition->Knowledge Point->Calculation Modules->Ratios and Proportions