Recall your d = rt, distance = rate * time.
now, let's say she lives "d" miles away, and so if Billy goes say at "r" mph fast to her house, he gets there in 1hr.
now, if he goes 20 mph slower, namely " r - 20 " mph, he gets there in 2 hours, same "d" miles.
now, let's say she lives "d" miles away, and so if Billy goes say at "r" mph fast to her house, he gets there in 1hr.
now, if he goes 20 mph slower, namely " r - 20 " mph, he gets there in 2 hours, same "d" miles.