14+0.08(t- 100)=30，
0.08t=24，
t=300，
Call time/minute, mode 1 usage fee/yuan, mode 2 usage fee/yuan.
t≤ 100 14 30
t=300 30 30
300 & ltt & lt500 14+0.08(t- 100)
t=500 46 30
t & gt500 14+0.08 30+0.06(t-500)
(2) When t & lt300, a cost-effective way.
When t=300, the two methods charge the same.
When t >; 300, the second way is cost-effective.