Am completely stuck on this question. would realy appreciate your guidance

Question 2 Consider the following Cobb-Douglas production function: y(K,L) = 20.810, where K denotes the amount of capital and L denotes the amount of labour employed in the production process. Let input prices be r for capital and w for labour. A firm seeks to minimize its cost of producing 10 units of output. a) By applying the Lagrangian method, derive the optimal demands for capital and labour. b) Derive the long-run cost function and plot it. c) Show that the Lagrangian multiplier 1 is equal to the marginal cost