Unless I'm missing something important here, all you have to do in order to solve this problem is use the target concentration of the solution and its volume to find how many milligrams of hemoglobin you need.
The concentration of the target solution is given as
Now, if you need this target solution to have volume of
#6color(red)(cancel(color(black)("mL solution"))) * "1.5 mg hemoglobin"/(1color(red)(cancel(color(black)("mL solution")))) = color(green)("9 mg hemoglobin")#
The answer is rounded to one sig fig, the number of sig figs you have for the volume of the target solution.