The original speed of a big car is 30 km / h, now it starts to accelerate evenly, increasing speed by 20 km / h The original driving speed of a large car is 30 km / h, now it starts to accelerate evenly, increasing the speed by 20 km / h; the original driving speed of a small car is 90 km / h, now it starts to decelerate evenly, decelerating by 10 km / h. how long does it take for the two cars to speed up equally? What is the speed at this time? (writing process)

The original speed of a big car is 30 km / h, now it starts to accelerate evenly, increasing speed by 20 km / h The original driving speed of a large car is 30 km / h, now it starts to accelerate evenly, increasing the speed by 20 km / h; the original driving speed of a small car is 90 km / h, now it starts to decelerate evenly, decelerating by 10 km / h. how long does it take for the two cars to speed up equally? What is the speed at this time? (writing process)

Let X be a process
30+20x=90-10x
30x=60
X = 2 hours
Speed = 30 + 20 * 2 = 70 km / h