In this case, red blood cells amount in the sample minus the amount of plasma. Red blood cells is 45% of total blood and plasma is 5.5ml. You need to find how many ml is 1% of blood. Then the equation would be
Red blood cells = total sample - amount of plasma
45%= 100% - 5.5ml
100%-45% =5.5ml
55%=5.5ml
1%= 0.1ml
After you found 1%=0.1ml , you can find out red blood cells volume or total sample volume.
Red blood cells volume = 45% x 0.1ml/%= 4.5ml
Total sample volume =100% x 0.1ml/% = 10ml
