1. what you know: the plane travels 42 miles in a quarter of an hour.
2. what you need to find out: the miles traveled in an hour.
ok, so how many quarters are in a whole? (look at the denominator of the fraction. the denominator is the bottom number of the fraction, which is four.)
since 42 is the value in 1/4 of an hour, 42×4 is the value is 4/4 or a whole hour. so find the product (the answer you get when you multiply two numbers) of 42 and 4.