Identify whether you would perform the following unit conversions by definition, by conversion factors, by geometry, or by scientific law.

a. How many square miles in a square kilometer?

b. How many microfarads in a farad?

c. What is the weight on Earth in N of an object with a mass of 10.0 kg?

d. How many square miles on the surface of the Earth?

Assume that on the surface of the Earth, g = 9.81 m/s² = 32.2 ft/s² (i.e., each to three significant figures). Make sure you are reporting the solution to the proper number of significant figures.