This question appear incomplete because of the absence of the value of the count of the ions inside the unit cell. To determine the mass (in grams) of LiCl in a unit cell, the formula below can be used
count of ions inside the unit cell = mass of LiCl ÷ molar mass of LiCl
Hence,
Mass of LiCl = count of ions inside the unit cell × molar mass of LiCl
Count of ions (Li⁺ and Cl⁻ ions specifically) inside the unit cell should have been provided in the question