The distance between piers a and b a motor boat sails against the river in 30 minutes and the same distance across

The distance between piers a and b a motor boat sails against the river in 30 minutes and the same distance across the lake in 10 minutes in how many minutes the distance between piers a and b a) raft b) a motor boat along the river

1-distance between A and B
1 / 30- the distance the boat sails against the current in 1 minute
1 / 10- swims on the lake in 1 minute
1 / 10-1 / 30 = 1/15 – the raft sails in 1 minute (current speed)
1/10 + 1/15 = 1/6 – the boat sails downstream in 1 minute
1: 1/15 = 15 (min) the raft floats between A and B
1: 1/6 = 6 (min) the boat floats downstream between A and B