In March, Josephine used 2,500 units of electricity at £0.09 per unit, plus a further 1,400 units at £0.05 per unit. In addition, she paid a standing charge. The total of the electricity bill for March was £319.
(a) Calculate the standing charge.
(b) Taking into account the cost of units and the standing charge, calculate the average cost per unit used in March.
(c) Taking into account only the cost of units, calculate the average cost per unit used in March.