i'm revising for an exam and have this question posed (this isn't homework) what is the maximal velocity for a clock being transported from london to new york if the time differance to a stationary clock should be less than 10^-8 seconds. i'm not allowed to use calculators. i've tried doing it by t=t'y, but get a velocity of 1/3c, which i think is much too high. anyone have any ideas? thanks.