Factor out the gcf
4x(x^2-16)
Then factor the inner binomial (difference of squares)
4x(x+4)(x-4)
Final answer: 4x(x+4)(x-4)
Well, the difference (or relative speed) is 3 mph. They get 12 miles apart in 4 hours.
1.40 is 140/100 = 7/5
7/5 divided by 4 is 7/5 multiplied by 1/4 so the solution will be 7/20