To put it simply we ca do the next procedure
12 E21/6E23 201 = 2 E-2 201 = 4.02 g
Remember please that Hg has two hundred.fifty 9 grams now weight of 6.022*10^23 atoms weigh two hundred.fifty 9 grams now remedy for a million.Then we do the procedure i showed you at the beginning an in that way you will have the result of 4.02g