An athlete preparing for a marathon runs 21.3 miles. How many kilometers did they run? (please give fourmula)

Which of the following is always a reactant in a combustion reaction? oxygen nitrogen hydrogen carbon

Which process does not require the presence of a physical substance in order to transfer heat? air in the atmosphere is heated by the ground. this warm air then rises, and cooler air falls. this is an example of what type of process? how is conduction different from radiation?

Apound is approximately 0.45 kilogram. a persons weighs 87 kilograms. what is the persons’s weight, in pounds, when expressed to the correct number of significant figures