1 mole requires 40.5 kJ
Approx Ar values used so I'll say I mole weighs 46.0g.
You should use the values you are given and quote the significant figures accordingly.
46.0g requires 40.5kJ
1g requires 40.5/46.0 kJ
98.6g requires (40.5/46.0) x 98.6 = 86.8g