The balanced reaction is:
CaCO3 = CaO + CO2
We are given the amount of CaCO3 to decompose when heated. This will be our starting point.
98.60 g CaCO3 ( 1 mol CaCO3 / 100.09 grams CaCO3) (1 mol CaO / 1 mol CaCO3 ) ( 56.08 g O2 / 1 mol CaO) = 55.25 g CaO