There are four major auto routes from boston to detroit
and six from detroit to los angeles. how many major
auto routes are there from boston to los angeles via detroit?

Here is the answer for the given question above. Since any of 4 routes from Boston to Detroit can be combined with any of 6 routes from Detroit to Los Angeles, we have to apply the product rule, which means that there are 6 x 4 = 24 major auto routes from Boston to Los Angeles via Detroit. Hope this answer helps.