To answer this question, we need to know first the unit conversion of each item in the choices such conversions are enumerated below:
1 centigram = 0.001 dekagrams
1 hectograms = 0.1 kilograms
1 grams = 1000 milligrams
1 dekagrams = 0.1 hectograms
From the choices, the correct unit conversion is the letter "B" which is "To find the number of hectograms in 4.5 kilograms, multiply 4.5 by 10". The solution is shown below:
4.5 kilograms * (1 hectograms / 0.1 kilograms), we need to cancel both kilograms such as the remaining unit is only the hectograms
4.5 * (1 hectograms / 0.1) where 1 divided by 0.1 is 10
4.5 * 10 hectograms
Therefore, 4.5kilograms should be multiplied by 10 in order to have hectograms as a unit.