Transition metals question-helpppp

This question refers to the chemistry of d-block elements in period 4. For each statement below, select the symbols of the correct elements.

Q). The element that has atoms with an average mass of 8.64 x 10^-23 g. Answer is Cr


This is the question I am stuck on, some help would be greatly appreciated!!!

Consider mass = Mr x moles, and the fact that there are 6.022 x 10²³ atoms in one mole of atoms – work out the Mr of one atom