There are 900 - 42 = <<900-42=858>>858 feet of path to line.
There are poles every 6 feet, so the company needs 858 / 6 = <<858/6=143>>143 poles.
The poles have to go on both sides of the path, so there will be 143 * 2 = <<143*2=286>>286 fence poles along the whole path.
#### 286