Show me the steps to solve: Bobby is a grad student at Wilton U$.$ He works in the Wilton U caf$$ two days per week and earns $$3,000$ during the year from doing this. He also received a $$15,000$ scholarship to cover his tuition, fees and books. And he received a $$10,000$ scholarship to cover his room and board.

How much of this $$28,000$ he received, in total, can Bobby exclude from his gross income for federal tax purposes?