A competitive firm uses two variable factors to produce its output, with a production function f(x1,x2) = (min {3x1,2x2}) 1/2. The price of factor 1, i.e. x1, is $3 and the price of factor 2, i.e. x2, is $4. Due to a lack of warehouse space, the company cannot use more than 12 units of x1. The firm must pay a fixed cost of $180 if it produces any positive amount but doesn't have to pay this cost if it produces no output. In long- run, the smallest integer price that would make a firm willing to produce a positive amount is (a) $12. (b) $24. (c) $36. (d) $48. (e) None of the above