First, we consider 63.52% and 36.48% for 100g of the compound.
So there are 63.52 g of Iron and 36.48 g of Sulfur.
Now it is necessary to pass these values to the amount of matter (mol). We do this by dividing each of the values found by their respective molar masses:
Iron: 63.52/55.845 = 1.14
Sulfur: 36.48/32.065 = 1.14
Now we can divide by 1.14:
Iron: 1.14/1.14 = 1
Sulfur: 1.14/1.14 = 1
Thus, the mpirical formula of this unknown substance is equal to
FeS
Answer: FeS