Two buses drove towards each other, the first traveled 90 km before the meeting, and the second traveled 20 km more

Two buses drove towards each other, the first traveled 90 km before the meeting, and the second traveled 20 km more, what is the distance between the cities?

Let’s designate the distance that the first bus traveled as S1, and the distance that the second bus traveled as S2.
By the condition of the problem, S1 = 90 km, and
S2 = S1 + 20 = 90 + 20 = 110 km.
Since the buses were traveling towards each other, adding the distances that the first and second buses traveled, we get the distance between cities.
Therefore, the distance S between cities:
S = S1 + S2 = 90 km + 110 km = 200 km.
Answer: the distance between cities is 200 km.