You buy a gallon of milk which will spoil in 4 days, However, you know for a fact that you will want glass of milk in 10 days. You put your milk onto a spaceship and blast it off at a speed V.
(a) What is the minimum speed at which the milk must be trawling such that it is still good when it returns to you in 10 days?
(b) How far has the milk traveled in your frame of reference?
(c) How far has the milk traveled in its frame of reference?