Question

how many milliliters of 125(v/v) aqueous propyl alcohol solution would you take to obtain 4.5ml of propyl alcohol​

Answer 1

A solution's volume by volume percent concentration,  % v/v , is a measure of how many milliliters of solute it contains in  100 mL  of solution.

In your case, a  12% v/v  solution will contain  12 mL  of solute for every   100mL  of solution.

This means that in order to have  4.5 mL  of solute, you need to have

4.5 mL of solute × $\frac{100ml of solution}{12ml of solute}$= 37.5ml of solution.

Thus, 37.5ml of 12%(v/v) aqueous propyl alcohol solution is needed to obtain 4.5ml of propyl alcohol​