Complex conversions between units may require using what type of conversion factor

Complex conversions between units may require using more than one type of conversion factor.

A conversion factor is a factor is used to convert the unit of measurement to another. A more complex one can be used to convert miles per hours into meters per second. Conversion factor always represents a fact. 

1. and 2. question: in which equation? or i don't understand you, 3. a), 4. c), 5. c), 6. b), 7. d), 8. d) if small number is underlined(behind symbol) , b) if big number is underlined(in front of symbol)9. what is underlined there? 10. c)