For a given substance, its tells you the mass occupied by one unit of volume of that substance.
In essence, is a measure of how well the molecules of a substance are packed in a unit of volume. In your case, the densities of the two substances are expressed in grams per milliliter, which means that a unit of volume will be
So, mercury has a density of
Your strategy here will be to use the density of mercury to find the mass that occupies
So, you will have - don't forget to convert the volume from liters to milliliters
$ 0.95 color(red)(cancel(color(black)("L"))) * (10^3color(red)(cancel(color(black)("mL"))))/(1color(red)(cancel(color(black)("L")))) * overbrace("13.546 g"/(1color(red)(cancel(color(black)("mL")))))^(color(purple)("density of mercury")) = "12,868.7 g"$
The volume of ethanol that will have an equal mass is
$"12,868.7" color(red)(cancel(color(black)("g"))) * overbrace("1 mL"/(0.789color(red)(cancel(color(black)("g")))))^(color(purple)("density of ethanol")) = "16,310.1 mL"$
Rounded to two and expressed in liters, the answer will be
$"16,310.1"color(red)(cancel(color(black)("mL"))) * "1 L"/(10^3color(red)(cancel(color(black)("mL")))) = color(green)("16 L")$