Answer:
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
