Consider the production of Good X. Good X is produced using only labor, which can be supplied by either humans or robots, with the production function given by X=f(H,R)=H + R. Humans and robots are perfect substitutes for each other. Suppose the wage humans earn is $15/hour and the wage robots earn is $6/hour. What is the cost function that producers face in this scenario? Answer 1-C(X)=15*X 2-C(X)=6*X 3-C(X)=21*X 4-C(X)=X/21