Find the molecular m of element knowing the solvent's Kf, m, freezing point and element's m & fp

After heating solid naphthalene to convert it to a liquid, an element is then dissolved in the naphthalene. If the Kf of naphthalene is 6.9 K/mc, its freezing point is 80 C, and its m is 7 grams. And if the element's freezing point is 70 C and its m is 0.6 grams, how would you calculate the element's molecular m?