We will need to use Avogadro's number (6.022*10^236.022⋅1023) to solve this problem. In case you don't know, Avogadro's number tells you how many molecules, atoms, or chemicals are in a mole of those molecules, atoms, or chemicals. So there are 6.022*10^236.022⋅1023 atoms of He in 11 mole of He atoms.
Now, let's get on with the problem. We will need to use dimensional analysis to convert from atoms of He (which was given) to moles of He (what we are trying to find):
9.033*10^23" atoms He"rarr"moles?"9.033⋅1023 atoms He→moles?
9.033*10^23" atoms He"((1" mole He")/(6.022*10^23 "atoms He"))=?9.033⋅1023 atoms He(1 mole He6.022⋅1023atoms He)=?
9.033*10^23color(red)(cancel(" atoms He"))((1" mole He")/(6.022*10^23 color(red)(cancel("atoms He"))))=?
Plug this into your calculator, and you should get a value of color(blue)(1.500" moles of He") with the appropriate number of significant figures (4).
I hope that helps!
