Ответ: 240/(x-10)-240/x=48/60=0.8(240/(x-10)-240/x)*x=0.8×2400/(x-10)=0.8×2400/(x-10)*(x-10)=0.8x*(x-10)2400=0.8x²-8x-0.8x²+8x+2400=0D=8²-4*(-0.8)*2400=7744×1=(√7744-8)/(2*(-0.8))=-50×2=(-√7744-8)/(2*(-0.8))=60 км в час