A circuit consists of a 15 Ω and a 30 Ω resistor connected in parallel across a battery of internal resistance 2 Ω. If 60 W is dissipated by the 15 Ω resistor, calculate
(a) the current in the 30 Ω resistor,
(b) the terminal p.d. and emf of the battery,
(c) the total energy dissipated in the external circuit in one minute and
(d) the quantity of electricity through the battery in one minute.