Since $$9$$ mugs $$=5$$ plates  $$45\div9=5$$ times of the above equation.  $$45$$ mugs $$=25$$ plates 
If $$5$$ plates weigh as much as $$9$$ mugs, then $$45$$ mugs weigh as much as~\uline{~~~~~~~~~~}~plates. 

a) $$18$$ 
b) $$25$$ 
c) $$72$$ 
d) $$81$$ 