Well, according to thedinosaurmuseum.com, the fastest ever running dinosaur(s) could run to up to (approx.) 60 km an hour. And according to sciencenetlinks.com, T. rex's ran approx. 45 miles an hour. To be able to subtract, you would have to find out how many kilometers in a mile. There are 1.60934 kilometers in a mile (round it to 1.6). So that means that a mile is slightly larger than a kilometer. Now you have to multiply 60 km by 1.6. Once you do that, subtract that number by 45. And there is your answer! I hope this has helped!