求救, 有關production function一問

first assume the firm face competitive market in both input and output markets.
also, let the production function be Xt=MtF(nt), while X is output, M is productivity, n is input, t is time subscrib.
further suppose that we have a learning-by-doing effect, so that we have another condition as: Mt+1 - Mt = dMtF(nt).
assume there is a constant interest rate r.

請問各位, 我應該如何寫出這間公司的profit function呢?