profit maximizing level of price and output from demand functions of two goods . finding revenue

Given the demand functions for two goods Px= 320 -4x + 2y and Py=  106 + 2x - 20y and a firms total cost function TC =4xy +40x 26y
1)Write down the equation for overall total revenue.
2) Find the values of Px, x, Pr, y, for which revenue is optimised, and use second order conditions to confirm it is maximum. Hence calculate the maximum total revenue
3) Write down the equation of the profit function
4) Determine the values x and y for which profit is optimised, and use second order conditions to confirm it is maximum. Hence calculate the maximum profit. Also calculate total revenue and the prices charged when profit is maximized