Answer:
Thailand:
Opportunity cost of computers = 300/20 = 15 tons of rice
US:
Opportunity cost of computers = 800/100 = 8 tons of rice
US has a comparative advantage in production of computers
Absence of trade:
Thailand consumes 150 tons of rice, it can consume = (300 - 150)/30 x 2 = 10 computers
US consumes 50 computers, it can consume = 400 tons of rice
After trade :
10 computers exchanged for 120 tons of rice
Thailand continues to consume 150 tons of rice, it will consume = 12 computers (=10 + 30/15)
US continues to consume 50 computers, it will consume = 440 tons of rice (=120 + 40 x 8)
Both would accept the proposal as both are better off with trade