Take 5.25 grams and give it proportionally to the carbon
0.9226 * 5.25 grams = 4.84 grams Carbon
Find the number of moles
(4.84 grams carbon)/(12.01 grams/mol) = 0.403 moles Carbon
The number of atoms in a mole of a substance is called Avogadro's number.
There are 6.022 * 10^23 atoms in one mole of anything
(0.403 moles Carbon) * (6.022 * 10^23 atoms/mole) = 2.43 * 10^23 atoms of Carbon