If you have 3 moles, what is that equal to numerically?

How many things are in 1 mole? Too mamy to count, so we weigh them. How much does 1 mole weigh?
From here it is just simple algebra. You can do it.

Avogadro's number is 6.022 x 10^23, which represents the number of constituent particles of a substance in a mole of that substance. Hence there are 6.022 x 10^23 molecules of H20 in a mole of water. The number of H20 molecules in three moles of water is 3 times Avogadro's number.

It depends on what you have three moles of. Look at the atomic weight and multiply it by three. If it's a compound add the atomic weights of the different elements and then multiply that number by three