Two buses left the station simultaneously in opposite directions. The speed of the first is 15 km / h

Two buses left the station simultaneously in opposite directions. The speed of the first is 15 km / h more than the speed of the second. What is the speed of each bus if the distance between them in 4 hours is 620 km ..

Let the speed of the second bus be x km / h, then the speed of the first bus is (x + 15) km / h. The second bus will cover 4 km in 4 hours. and the first – 4 * (x + 15) km. After 4 hours, the distance between them will be (4x + 4 * (x + 15)) km or 620 km. Let’s make an equation and solve it.
4x + 4 * (x + 15) = 620;
4x + 4x + 60 = 620;
8x = 620 – 60;
8x = 560;
x = 560: 8;
x = 70 (km / h) – speed of the second bus;
x + 15 = 70 + 15 = 85 (km / h) – the speed of the first bus.
Answer. 85 km / h, 70 km / h.