Answer:
60kph
Step-by-step explanation:
Distance = Rate X Time
640 = r x 4+ (r+5) x 7
640 = 4r + 7r + 35
640=11r + 35
640 - 35 = 11r
605 = 11r
r = 605 / 11
r= 55 kph
r=55 =5 =60 kph is the speed of the train
To see if the answer is right: 55 x 4 + 60 x 7 = 220 + 420 = 640 km
