For this item, the ∆t will be the value of temperature difference that the substances will experience once subjected to same amount of heat. The heat is equal to,
H = mcp∆t
where H is heat, m is mass, cp is specific heat, and ∆t is temperature difference.
The compounds given, despite having the almost the same molecular weight, will have different ∆t because of the different intermolecular forces present especially in the alkyl groups present.