Up a mountain, Stephen covered 3/4*40000 = <<3/4*40000=30000>>30000 feet.
Coming down, Stephen covered another 30000 feet, making the total distance covered in one round to be 30000+30000 = <<30000+30000=60000>>60000.
Since Stephen made 10 round trips up and down the mountain, he covered 10*60000 = <<10*60000=600000>>600000
#### 600000