Given that I no not see any explanation in the previos answer, I think you can benefit of this.
Exothermic refers only to the fact that the reaction releases energy in the form of heat when occurs. So, the enthalpy is higher at start and lower and the end.
Seen in this way, you can deduct that the change in enthalpy is negative, which is what the third option says.
The percent of boys in the class is 40% because 16 + 24 = 40 (the entire amount of kids) 16 / 40 = .4 then move decimal twice to the right for percentage which gives you 40%
