(1)180×0.573+(300-180)×(0.573+0.05),
=103.14+120×0.623,
=177.9(元);
答:应交电费177.9元.
(2)设卡帕一家七月份共用电x度,则:
180×0.573+(400-180)×(0.573+0.05)+(x-400)×(0.573+0.3)=327.5,
240.2+(x-400)×0.873=327.5,
x-400=(327.5-240.2)÷0.873,
x-400=100,
x=100+400,
x=500
答:那么他们一家七月份共用电500度.