(1)根据题意,y=150×0.4983+(240-150)×(0.4983+0.05)+(x-240)×(0.4983+0.3),
=77.745+49.347+0.7983x-191.592,
=0.7983x-67.5,
即y=0.7983x-67.5;
(2)x=300时,y=0.7983×300-67.5,
=239.49-67.5,
=171.99.
答:小张家7月份应支付的电费171.99元.
(1)根据题意,y=150×0.4983+(240-150)×(0.4983+0.05)+(x-240)×(0.4983+0.3),
=77.745+49.347+0.7983x-191.592,
=0.7983x-67.5,
即y=0.7983x-67.5;
(2)x=300时,y=0.7983×300-67.5,
=239.49-67.5,
=171.99.
答:小张家7月份应支付的电费171.99元.