Landlord, first of all: (700× 3 = 2100m2100-400 =1700m) This is the correct answer. Let me explain my thoughts.

When we first met, two ships sailed on the river 1, and ship A traveled 700 meters. After the second meeting, Party A and Party B made a total of three trips on the river. That is to say, during these three trips, Party A traveled three 700 meters (700×3=2 100 meters). Since one of the three 700 meters reached the other side and returned to 400 meters, it was necessary to subtract 400 meters and 2/kloc. It's best to draw a schematic diagram when telling children to make them easier to understand. Thank you! ! !