1.设s=kt+b,(3.5<=t<=4.5) 则有15.5k+b=60 16.5k+b=0==>>k=-60,b=990==>>s=-60t+990(15.5<=t<前中=16.5)2. 25=-60t+990==>慧迟山>t=193/12,即旦模16点5分根据题意可知从8点25分到16点5分没信号