The conversion factor always has a value of 1. It is a fraction with the numerator equal to the denominator -- only the units are different.
The numerator units are the units you're converting <u>to</u>: millimeters. The denominator units are the units you're converting <u>from</u>: centimeters.
You know that 1 cm = 10 mm, so when you arrange the fraction as described, the conversion factor you're multiplying by is ...
For this case we have the following equation: V = I * R Where, V: voltage I: current R: resistance By clearing R we have: R = V / I Substituting the values: R = (20) / (0.57) R = 35.09 Ohms Answer: The resistance of the light bulb is: R = 35.09 Ohms