Im going to give you the process in such a way that you get the answer and it will be very easy. What you need here is the formula n = N x m / W
N = Avagadro's number,
m = mass
W = molecular weight
So the process will be like this:
n = 6.07 x10^27 x 2.4 / 18
Use your calculator and then you will have your answer