The formula to find moles is:
n = m / M
m stands for mass, which in this case m = 64.92g
M stands for molar mass. You would need to look at the periodic table for each element of AgNO3 and add them together to get M.
n = 64.92 / 107.9 + 14.01 + 3(16)
= 0.382084...
= 0.38 moles (2 d.p)
Hope this helped!
