Organs often have a combination of pipes with one and two closed ends. For a pipe of fixed length, will the first harmonic of the pipe with one closed end achieve a higher or lower pitch than the first harmonic of a pipe with two closed ends?

Automobile fuel efficiency is often measured in miles that the car can be driven per gallon of fuel (mpg). heavier cars tend to have lower fuel efficiencies (lower mpg ratings). which variable (weight or fuel efficiency) is most naturally considered the explanatory (predictor) variable in this context?