First convert each mass to moles by dividing by the molar mass.
0.347g Oxygen = 0.022 moles
0.260g Carbon = 0.022 moles
1.537g Chlorine = 0.043 moles
Divide each by smallest mole vale (0.022)
Oxygen = 0.022/0.022 = 1
Carbon = 0.022/0.022 = 1
Chlorine = 0.043/0.022 = 2
Therefore the empirical formula is COCl2