Six different airlines fly from New York to Denver and

seven fly from Denver to San Francisco. How many dif$-$

ferent pairs of airlines can you choose on which to book

a trip from New York to San Francisco via Denver, when

you pick an airline for the flight to Denver and an airline

for the continuation flight to San Francisco?

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 De$-$

troit?