You have to convert a proper fraction to a decimal. (The proper fraction will be the answer you got for number 21.)
Lets say that the proper fraction is one half.
A decimal is always over 1. You have to convert the denominator to 1. In this case, you divide 2 by 2 to make 1. Whatever you do to the bottom you have to do to the top. 1÷2=0.5