Plz help i am stuck on this

During the past 150 years in the united states, how did energy consumption compare to population growth

How does the strength of the electrostatic force between an electron and a proton compare to the strength of the gravitational force between them?

When oxygen reacts with hydrogen, it has the capacity to release 29 kilojoules of energy. inside a fuel cell, oxygen reacts with hydrogen to produce 23 kilojoules of useful energy. the rest of the energy is lost as heat. what's the efficiency percentage of the fuel cell?