You're not spamming.  This is a chemistry question more
than a mathematics question.

mL and cubic centimeters are both measures of volume.

The rule to remember about NaCl solutions is this:

If N grams of table salt NaCl is dissolved in enough water 
to make 100 mL (total volume) of solution, then the salt 
concentration is N%.

So since the table salt concentration is 20%, if there were 100 mL
of salt solution, then it would contain 20 grams of table salt. 

But there are only 45 mL of table salt solution, so

 
 
 

So there are 9 grams of table salt in the solution.

The density of salt is 2.16 g/mL.





So the number of mL of salt is therefore 4.167 mL.  

Edwin