Answer:
So, exist 12 different trips can be made from city X to city Z passing through city Y.
Step-by-step explanation:
We know that there are three roads from city X to city Y and four roads from city Y to city Z.
So if we chose the first path from city X to city Y, then we have 4 more options to go from city Y to city Z.
So if we chose the second path from city X to city Y, then we have 4 more options to go from city Y to city Z.
So if we chose the third path from city X to city Y, then we have 4 more options to go from city Y to city Z.
We get: 4+4+4=12.
So, exist 12 different trips can be made from city X to city Z passing through city Y.