The ratio of number of apples to number of pears in a box was $$3 : 4$$. When $$36$$ pears were replaced by $$36$$ apples, the number of apples became $1\frac{1}{2}$ of number of pears. How many apples were there at first?~\uline{~~~~~~~~~~}~ 
Overseas Competition->Knowledge Point->Combinatorics->Patterns of Figures->Change of Quantity