Can you give me some step-by-step instructions for this math problem: Tonya has opened a lemonade stand selling lemonade in small, medium, and large cups at $1, $2 and $3 respectively. At the close of business she ended up making $50.  As she went back through her inventory she noticed that she sold $11 worth of small lemonades and $24 worth of medium lemonades. How many cups of large lemonade did Tonya sell?