Consider a single-product firm that is a price-taker in all of the markets in which it participates. This firm uses one input (labour) to produce output of its product (widgets). Its production function, f:\mathbb{R}_{ }\longrightarrow\mathbb{R}_{ }, is given by f\left ( L ight ) = 4\sqrt{L}, where L is the number of hours of labour that is used by the firm. The price of widgets is twenty-eight dollars per widget. The wage rate for labour is seven-dollars per hour. If the firm wants to maximise its profit, it should use \cdots hours of labour