车费是分段函数,f(s)=10,s<=410+1.2(s-4)=1.2s+5.2,410+1.2(15-4)+x(s-15)=23.2+x(s-15)于是f(51)=23.2+x(51-15)=23.2+36x=77.2解得x=1.5
10+11*1.2+(51-15)*x=77.2===>x=1.5
