Capacitances of 10 mF and 20 mF are connected in parallel, and this pair is then connected in series with a 30-mF capacitor. What is the equivalent capacitance of this arrangement?

Kirchhoff's junction rule: At any junction point, the sum of all the currents entering the junction must equal the sum of all the currents leaving the junction.
Kirchhoff's loop rule: The sum of the changes in potential around any closed path of a circuit must be zero.