Answer:
C = 80pF
Step-by-step explanation:
The total capacitance of 4 capacitors connected in series is given by:
[tex]Ct = \frac{1}{1/C1 + /C2 + 1/C3 + 1/C4}[/tex]
[tex]Ct = \frac{1}{1/C + /C + 1/C + 1/C}[/tex]
[tex]Ct = \frac{1}{4/C}[/tex]
[tex]Ct = \frac{C}{4}=20pF[/tex]
Solving for C:
C = 4*20pF
C = 80pF