Mr Tan made some fish balls. He sold $$\frac34$$ of the fish balls in the morning and $$\frac13$$ of the remaining fish balls in the afternoon. He made another $$506$$ fish balls and had twice the number of fish balls he made at first. How many fish balls did he make at first? 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Finding the Base