Three resistors of 5 Ω, 6 Ω and 7 Ω respectively are connected in parallel. This combination is connected in series with another parallel combination of 3 Ω and 4 Ω . If the complete circuit is supplied from a 20 V source, calculate
(a) the total resistance,
(b) the total current,
(c) the p.d. across the 3 Ω resistor and
(d) the current through the 4 Ωresistor.