One crew can seal a parking lot in 9 hours and another in 12 hours. how long will it take to seal the parking lot if the two crews work together?

First crew = 1 lot in 9 hours, therefore 1 hour =  of the lot.
second crew = 1 lot in 12 hours, therefore 1 hour =  of the lot.
In one hour, both can seal () of the lot, which is 

= 1 hour
=  hour
= 5 hour

So they need 5 hour if they work together.

╔═⋄═◇═◈═❖═✧═☆═✧═❖═◈═◇═⋄╗✧   ok, now this, is epic.╚═⋄═◇═◈═❖═✧═☆═✧═❖═◈═◇═⋄╝

It’s hard to understand what you put.. can you show a picture ?