2,80 * 3/2.5 = 96 km

3, 40 kilometers, 40* 1 1/80=5.5 hours.

4、(5/8+2/27)*8+ 1 1/27=5+ 16/27+ 1 1/27=6

9/20/[3/2(0.4+4/5)]=9/ 16

4.8*3.9+6. 1*4/5= 18.72+4.88=23.6

5, 8 * 6000000 =4800000 cm =480 km, 480 km /4000000= 12 cm.

6, 6*6000000=36000000 cm =360 km, 360/( 100+80)=2 hours.

7. Freight car speed = (55/11) * 9 = 45 km/h, railway length of A and B = (55+45) * 5 = 500km.