Verified answer

That is a 3 Step Mole Equation

Here's the set up:

5.13 x 10^21 atoms x (1 Mole)/(6.02x10^23) x (atomic mass of Platinum)/ (1 mole)

EDIT:

An easy way to do the calculation is to (5.13x10^21) (109.08g)

all divided by (6.02x10^23)

I got 1.66g, so if you get rid of the x10 youll be fine, just a minor calculating error.