Answer: 362880
Step-by-step explanation:
Given : A contractor wishes to build 9 houses, each different in design.
he place these houses on a street if 6 lots are on one side of the street and 3 lots are on the opposite side.
Choices to arrange first lot = 9
After first house is designed , Choices to arrange second lot = 8
After second house is designed , Choices to arrange third lot = 7
and so on.....
So the total number of ways to arrange 9 lots will be :-

Hence, the required number of ways =362880