Can someone help me with this question?

Suppose that there is a tax t on the sales of the firm, so that the firm only gets (1 - t ) times the

quantity produced. Show that the return to capital is now (1 - t ) . MPK. What is the new optimality

condition of the firm which determines the target capital stock. By graph show how an increase in

the tax on capital will affect the optimal capital stock and hence investment.