Answer:
A
Explanation:
its a because that is the first thing you do
1st one
2_2_2
2nd one
3_1_1_3
i looked it up
16.05 amu
12.011 rounds to about 12.01 and 1.008 rounds to about 1.01 so when adding you'd do [12.01 + (1.01×4)]= 16.05