If $$5$$ plates weigh as much as $$9$$ mugs, then $$45$$ mugs weigh as much as~\uline{~~~~~~~~~~}~plates. 
Overseas Competition->Knowledge Point->Calculation Modules->Basic Concepts of Equation->Equivalent Substitution->Algebraic Expressions
Since $$9$$ mugs $$=5$$ plates  $$45\div9=5$$ times of the above equation.  $$45$$ mugs $$=25$$ plates 