（1）a=60
(2)六月份用了100度,应交43.2元
(1)0.4a+(x-a)x0.48=84
(2)0.432x=0.4x60+(x-60)x0.48有过程吗？（1）0.4a+(84-a)x1.2x0.4=350520.4a+0.48x84-0.48a=35.520.48x84-0.08a=35.5240.32-0.08a=35.520.08a=40.32-35.520.08a=4.8a=60(2）0.432x=0.4x60+（x-60)x0.480.432x=24+0.48x-28.8-0.048x=-4.80.048x=4.8x=100100x0.432=43.2