Answer:8 barrels of oils per pair of shoe
Explanation:Greece and swizerland will need an average price by which they can both gain from trade.To ascertain the average price is by adding the 4 barrels of oil which Greece can forfeit and the 10 barrels of oil which Switzerland could also forfeit if it were into producing shoes.10+ 4 = 14/2 which almost 8 barrels to be given in exchange in other ensure a fair trade between both trading partners.