Here's a verbatim section of the problem: " The source contains carbon isotopes of mass numbers 12, 13, 14 from a long-dead piece of a tree. (To estimate atomic masses, multiply by 1.67x10^-27kg). " My question is isn't the 12, 13, & 14 in the atomic mass units already (Carbon-12 has an amu of 12)? Why would I need to multiply? And if I do need to multiply, should I leave it in kg or convert to g? Thank you.