Two trucks simultaneously meet each other at a speed of 840 km, the speed of the first is 64 km / h

Two trucks simultaneously meet each other at a speed of 840 km, the speed of the first is 64 km / h, and the second is 7/8 of the speed of the first, after what time they will meet.

Let’s solve the task of actions with explanations.
1) 64 * 7/8 = (64 * 7) / 8 = (8 * 7) / 1 = 56 kilometers per hour – the speed of the second truck, so its speed is 7/8 of the speed of the first truck, and the speed of this truck is 64 kilometers hour;
2) 64 + 56 = 120 kilometers per hour – the speed of convergence of two trucks, as they move towards each other at speeds of 64 kilometers per hour and 56 kilometers per hour;
3) 840: 120 = 7 hours – after this time the trucks will meet, so their approach speed is 120 kilometers per hour, and the distance is 840 kilometers.
Answer: in 7 hours.