For some reason we might discuss elsewhere students who (I presume) grasped simple proportion in early years at school can't do it any more later when it is called chemistry.
It is essential to know and understand whence comes the formula KE = (3/2) RT . If you had been asked to calculate KE from scratch you would need to be given R (or to be able to calculate it from something else you know, like a mole occupies 22.4 l at STP). You can calculate R also from the information given in the exercise.
But here you don't need to even consider R. R is independent of temperature. (3/2) is also the same at all temperatures(!). KE is proportional to absolute temperature. You have a ratio of temperatures, what is the ratio of KEs?
(Added - and this cancelling of things that are constant is already there hidden away in the problem because they haven't told you how much of the gas there is - if it doesn't change you don't need to know that either.)
(A separate point is that the temperature scale, practical origins understandable, is in theoretically rather irrational units, degrees, that depend on theoretically complicated and I believe incompletely understood or calculable properties of particulat substance, water . As Feynman pointed out, we might have defined temperature in joules/mole and in that case R would have been 1).