Answer:
R = 20E-6 m radius of cell
A = 4 π R^2
A = 4 π (2.0E-5)^2 = 4 π * 4.0E-10 = 5.02E-9 m^2
A = 5.02E-9 m^2 = 5020E-6 mμ
Apparently, (b) is the answer being looked for.
9.5m questions
12.2m answers