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A firm uses labor (denoted by L) and computers (denoted by K) to design apps (in this case the output). The number of apps is denoted by Q. The firm's production function is Q(K,L)=9L^(1/3) K^(2/3). The price of labor (w) is $5 and the price of capital (r) is $20. The marginal cost is:

30

10/3

2/3Q

(10/3)+(40/3)