At a bakery, muffins and donuts were sold at $ $6$ for $3$ and $ $10$ for $7$ respectively. Amy had some money. She spent $\frac{1}{2}$ of her money to buy some donuts and the remaining of her money on some muffins. She bought $54$ more donuts than muffins. How much money did Amy have at first? 
Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle