Your first step is determining how many gram of KCl are in every mole of KCl. This can be done by simply looking at K and Cl's atomic mass on the Periodic Table. You add K's atomic mass (39.1g) with Cl's atomic mass (35.45g) to determine that the mass of one mole of KCl is 74.55g. Because you have 10 moles of KCl you multiply 74.55g by 10 to reach your answer of 745.5g.