Answer :
2y(4z)=8yz
each major road of city y you have 4 different routes so if there're 2 routes of city y then double the number of routes and you get 8 different roads to travel in from x to z through y
each major road of city y you have 4 different routes so if there're 2 routes of city y then double the number of routes and you get 8 different roads to travel in from x to z through y