suppose you can mow a lawn in two hours and wash cars in the same amount of time. Your neighbor, Mr. Gedye, can mow a lawn in one hour. In order for him to have a comparative advantage in mowing lawns, how many cars must he be able to wash in two hours

we can assume that you can mow a lawn in 2 hours and was 4 cars during the same 2 hours.

your opportunity cost of mowing a lawn in 2 hours = 4/1 = 4 cars

your neighbor can mow a lawn in just 1 hour, so he can mow 2 lawns in 2 hours:

in order for him to have a comparative advantage in mowing lawns, his opportunity cost of mowing a lawn in 2 hours should be lower be lower than yours. So x/2 < 4, that means that x < 8. If your neighbor washes 7 or less cars in 2 hours, then he will have a competitive advantage in mowing lawns. e. g. 7/2 = 3.5 cars; 6/2 = 3 cars, etc.

You can introduce any number to the amount of cars washed per 2 hours, all you need to do is adjust: x/2 < the number of cars you decide