Please solve on paper so I can follow the steps

Find the stationary points of the following functions, and determine whether each is a maximum, minimum or saddle point. (a) z=x2 y2 +4y3x+50 (b) 2 = 2x5y +5x2 +2y2+4xy +1000 A rm charges different prices for its good to its domestic and export markets. In the domestic market its demand function is given by P = 20 2Q D while in the export market its demand function is given by P =15 1.5QE. The total cost function is TC = 5(QD + QE ). i) What level of output should the rm sell in each market in order to maximise prot? [hint total prot = Total Revenue Domestic market + Total Revenue Export Market - Total Cost] ii) What price will the rm charge in each market if it is to maximise its prots