4. (5%) Consider a representative firm in a perfectly competitive market using three inputs to produce its output: labor \( (L) \), capital \( (K) \), and material \( (M) \). The production function is given by \( f(L, K, M) = L^2 K^2 M^2 \). Suppose the unit price of labor, capital, and material are \( w = 1 \), \( r = 1 \), and \( m = 1 \), respectively. Each firm is assumed to solve the cost minimization problem given the capital level \( K = 1 \). The short-run cost function of each firm is _(4a)_ with efficient scale _(4b)_.