Mr. K started the day with $18.50 in his pocket. Nick gave him $2.75 to buy some coffee (thanks, Nick!). Mr. K then spent $4.35 at the coffee shop. When he returned to class Mrs. Spangler gave him $6.50 to watch her class for a few minutes (kinda weird, but ok). After school, Mr. K went back to the coffee shop and spent $9.75. How much money did he have at the end of the day?