M or molarity is (moles of solute)/(liters of solution)
0.812 M of Sodium Cyanide = 0.812 moles / Liters
To find the number of moles of sodium cyanide, we need the volume of the solution which is 145.6 Liters.
Multiplying the Molarity and the Volume together will result in the moles of solute:
0.812 M x 145.6 Liters =118 moles ( 3 sig figs )