Hi, I was confused about what rms speed means.

ohh this question is actually from  gases chapter.
µ _rms = √(3RT/M)
Here M is the molar mass of He which you have to take in SI units means kg/mol
R is universal gas constant = 8.314 J/mol.K
T is temperature in K.
Try to plugin values in the above equation.

oh ok, that makes sense