Figure 9 shows a diagram of a red blood cell from a turtle and a diagram of a red blood cell from a human - Edexcel - GCSE Biology Combined Science - Question 5 - 2018 - Paper 1

To find the length of the magnified image, use the formula:

$$ext{Magnified Length} = ext{Actual Length} imes ext{Magnification Factor}$$

Substituting the given values:

$$ext{Magnified Length} = 20.5 ext{ µm} imes 400$$

This gives:

$$ext{Magnified Length} = 8200 ext{ µm}$$

To calculate the actual width of the human red blood cell, we need to reverse the magnification process:

ext{Actual Width} = rac{ ext{Magnified Width}}{ ext{Magnification Factor}}

Using the given data:

ext{Actual Width} = rac{3.08 ext{ nm}}{400}

Calculating this:

$$ext{Actual Width} = 0.0077 ext{ nm} = 7.7 imes 10^{-3} ext{ nm}$$