A tiny pencil mark just visible to the naked eye contains about 3 * 1017 atoms of carbon. what is the mass of this pencil mark in grams?

The number of carbon atoms in the pencil mark is 3X1017 atoms of carbon The atomic weight of carbon is 12.01 amu, so 12.01 g of carbon contains 6.022X1023 atoms. Thus equation: 12.01 g carbon / 6.022 X 1023 atoms (3X1017 atoms) (12.01 g carbon / 6.022X1023 atoms) - the atoms cancel out (3X1017) (12.01g carbon/6.022X1023) divide and multiply = 6x10-6g carbon The mass of this pencil mark in grams is 6x10-6g carbon