Answer
$10 billion
Work Step by Step
Labor is wages, land is rent, and capital is interest. You begin with 100 billion dollars. Subtract 60 billion for wages (labor) and you’re left with 40 billion. Subtract from that 10 billion for rent (land) and you have 30 billion. Finally, subtract 20 billion for interest (capital) and 10 billion is left for the last remaining factor of production, entrepreneurial ability.