To what temperature must it be raised to triple the rms speed of its molecules?

Formula for RMS velocity (C) is

C=sq. rt (3RT/M)

So, C directly proportional to T in kelvin (273+20=293)

So, C1/C2=T1/T2

C2=C1XT2/T1

3C1=C1XT2/T1

3=T2/T1

T2=3XT1

T2=3x293

T2=2637k = (2637-273) = 2364oC

this is the answer I think