Compare the amount of thermal energy needed to melt a solid and the amount of thermal energy needed to freeze the same liquid

To melt a solid, energy must be input into the solid to give the molecules high energy to disrupt the lattice bonds and change phase. To return the liquid to solid, the same amount of energy used in melting is required to be removed from the liquid, ideally. This is assuming there is no loss of energy in the process.

10 years is the answer

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)