Think about what density means.
As you know, density is defined as mass per unit of volume. Simply put, the density of a solution will tell you what the mass of one unit of volume of that solution will be.
In your case, the mass is expressed in grams and the volume in milliliters.
This means that your unit of volume will be
#1 color(red)(cancel(color(black)("mL"))) * "0.5 g"/(75color(red)(cancel(color(black)("mL")))) = "0.006667 g"#
This means that the solution's density will be equal to
I'll leave the answer rounded to two sig figs, despite the fact that you only gave one sig fig for the mass of the solution.