Ladder #240 is five finishes in a row: 2, 45, 66, 95 and 108. You get one turn of three darts for each, and every finish has to end on a double or the bull.
2 is a straight double: D1. A miss into the single leaves an odd number, so the next dart has to set up a double before you can finish. 45 is a two-dart finish: 5 D20.
66 is a two-dart finish: T18 D6. 95 is a two-dart finish: T19 D19. 108 needs all three darts: T17 17 D20. If the first dart misses its treble, the board will show the new route straight away.
At best the five finishes need 10 darts out of 15. Your result counts the finishes you make first and the darts you used second. The middle finishes decide this ladder. Choose the route that leaves a double after a missed treble; the suggested routes do that wherever they can.