7.1
Use the formula of a circle. The radius is 1.5 and squared that is 2.25. Multiply that by 3.14 for your answer.
7x12= 84
1+6=7
12=12
So the area is 84
If there are two hydrogen atom molecules in one atom of water you'd do 51 times 2, getting you 102 hydrogen atoms in 51 water molecules.