Ahydrocarbon c₄h₁₀ has a boiling point of 0, another hydrocarbon c₆h₁₄ has a boiling point of 69. what would you expect the boiling point of c₈h₁₈ to be?

If the trend is linear, that is boiling point increases by a constant amount for each additional saturated carbon, the boiling point of octane would be 69*2 because you are adding two saturated carbons. So the predicted boiling point is 138C, which is very close to the literature value