Conversions are made best as follows:
1 m = 100 cm, hence: 1 m^2 = (100 cm)^2 = (100)^2 (cm)^2 = 10000 cm^2
Similarly:
1 inch = 2.54 cm, hence 1 inch^3 = (2.54)^3 cm^3
Also:
1 mile = 1600 m, hence 20 mile/hour =
20 x 1600 m /(3600 sec) = (20 x 1600 / 3600) m/sec
Good luck!