The amount of red blood cells in a blood sample is equal to the total amount in the sample minus the amount of plasma. what is the total amount of blood drawn? red blood cells = 45% plasma = 5.5 ml

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

B. because the 7 represents "seven times", x represents "a number", 12 represents "plus twelve", and -4 represents "minus four"