Analysis: A walked from place A to place B. When we first met, it was "90km away", which means that A walked 90km when we first met. Because of the "two encounters", * * * walked three times, which means that A must have walked three "90km" when meeting for the second time. That is to say, A still walked 50km, twice as much as AB.

(90× 3+50) ÷ 2 =160km

The distance between AB sides is 160km.