Answer :
according to the 55 m/min speed, in 3 minutes, he should have traveled 165 m.
Since he only went 135 m, that means the water moved against him for 30 m. That also happened in 3 min so the water is moving against him at 10m/min.
Since he only went 135 m, that means the water moved against him for 30 m. That also happened in 3 min so the water is moving against him at 10m/min.