So in order to find a solution's volume by volume percent concentration, all you need to do is to figure out how many milliliters of solute are present for every
In this case, you know that the total volume of the solution is equal to
#overbrace("45 mL ethanol")^(color(blue)("volume of solute")) + overbrace("125 mL water")^(color(blue)("volume of solvent")) = overbrace("170 mL solution")^(color(blue)("volume of solution"))#
You know that this solution contains
#100 color(red)(cancel(color(black)("mL solution"))) * "45 mL ethanol"/(170color(red)(cancel(color(black)("mL solution")))) = "26.47 mL ethanol"#
Therefore, you can say that this solution is
#color(darkgreen)(ul(color(black)("% v/v = 26% ethanol")))#
The answer must be rounded to two sig figs, the number of sig figs you have for your values.