Maybe this example could help you to understand this problem.
https://image.slidesharecdn.com/121howmanyatoms-091201144624-phpapp02/95/12-1-how-many-atoms-17-728....
Atomic number refers to the proton number of the atom itself. Number of electrons in an atom (an atom that is not reacted with any other molecules / Just the atom alone), is the same as the number of protons, because each electron has 1 negative charge, and each proton 1 positive charge, where they cancel out on each other to become a neutral charge.
So, when atomic number is 6, proton number is also 6, and number of electrons will also be 6 in that atom.
Hope this helps! :)
M=43lb = 19,5kg
If 115mg --------- is for --------- 1kg
so
x ---------- is for --------- 19,5kg
x = 19,5kg * 115mg / 1kg
x = 2242,5 mg
