please help

Find the base for the following items.


1.) 50 is 20% of what number?


2.) 50 is 20% of what number?


3.) 18 is 331⁄3% of what number?


4.) 4 is 1% of what number?


5.) 5% of what number is 90?


6.) 162⁄3% of what number is 72?