First, determine the amount of substance in moles by dividing the given amount in grams by the molar mass.
17.8 grams LiF x (1 mole / 25.94 grams LiF) = 0.686 moles LiF
Divide this amount of substance by the volume of the solution in liters.
molarity = 0.686 moles LiF / 0.915 L sol'n
The molarity is therefore, 0.75 M.
