You can use the pythagorean theorem. Now lets write out what we know.
Shorter leg = x Longer Leg = x + 7 Hypotenuse = x - 7
Now solve for x x = 28 Since you know x = 28, which is the shorter leg, you can solve for the rest by just plugging in 28 where x is located. For instance, longer let is x + 7 so 28 + 7 = 35
In 4 hours they will be 400 miles apart 4 times 55 is 220 and 4 time 45 is 180 since there going in opposer directions add the miles together and it equals 400 so it takes 4 hours