Solution:
We know that the Avogadro number tells us that a mole of any substance contains 6.022 * 10^23 atoms.
so,
we have to divide the number if carbon atoms by Avogadro number to get the number of moles.
5.7 * 10^21/6.022*10^23
=9.47*10^(-3)moles of carbon
To determine the mass in grams of 9.47*10^(-3)moles of carbon.
We have to multiply this number by the molecular weight of carbon
=9.47*10^(-3)moles of carbon*12.01g/mol
= o.11g of carbon.