If free trade will benefit all nations in the long run, why do nations so often establish barriers, like tariffs, to make free trade impossible?

Owns a machine that can produce two specialized products. production time for product tlx is two units per hour and for product mtv is four units per hour. the machine’s capacity is 2,100 hours per year. both products are sold to a single customer who has agreed to buy all of the company’s output up to a maximum of 3,570 units of product tlx and 1,610 units of product mtv. selling prices and variable costs per unit to produce the products follow. product tlx product mtv selling price per unit $ 11.50 $ 6.90 variable costs per unit 3.45 4.14 determine the company's most profitable sales mix and the contribution margin that results from that sales mix.