Ten years ago, Sam, a real estate agent, purchased a piece of land for $50,000. His intention at that time was to build a rental building on the land and use it to earn rental income, which he did four years ago. In the current year, he sold the land and building for $100,000 and $80,000 respectively after receiving an unsolicited offer. Is the proceeds from the sale of land on account of capital or business/ordinary income? Provide justification.