Explain that rational decisions occur when the marginal benefits of an action equal or exceed the marginal costs

Rational decision simply means a decision based on logic. It would be logical to say that people would always prefer more benefits than the cost they will be expending. Rational decisions indeed occur when the marginal benefits of an action equal or exceed the marginal costs. No person would make a decision that would incur a loss in his part. Therefore, in order to say that you were able to have a rational decision, you have to bear in mind the profit you can gain out of it. Example of this is the decision on additional worker. Suppose you are paying $20 per worker and they produce 5,000 units. If you are to add additional worker, you will incur an additional $20 but it will also increase the production output to 8,000 units. Therefore, it would be a rational decision to employ another worker since the benefits would exceed the cost. 

for many centuries there were important factors which the economies of the muslim empires developed increasingly. they applied economic procedures in production, investment, finance, taxation and property. they used to tax certain goods (for example: harvest), they charged interest on money lent, they signed contracts with merchants; they relied on a common currency, and they used checks as well as promissory notes. with the money collected by means of taxation, the government provided the needy with an income. in addition, trading networks covered huge distances, so far regions started to have contact and exchange goods. this trade network covered areas of asia, africa and europe.