An atom of argon has a radius rAr = 71. pm and an average speed in the gas phase at 25°C of 249.⁢/ms. Suppose the speed of an argon atom at 25°C has been measured to within 0.010%. Calculate the smallest possible length of box inside of which the atom could be known to be located with certainty.

Write your answer as a multiple of rAr and round it to 2 significant figures. For example, if the smallest box the atom could be in turns out to be 42.0 times the radius of an atom of argon, you would enter "42.rAr" as your answer.