l rotary engine, ltd., produces four-and six-cylinder models of automobile engines. the firm’s profit for each four-cylinder engine sold during its quarterly production cycle is $1,800 - $50x1, where x1 is the number sold. hinkel makes $2,400 - $70x2 for each of the larger engines sold, with x2 equal to the number of six-cylinder engines sold. there are 5,000 hours of production time avail-able during each production cycle. a four-cylinde