Checkout ladder #247 climbs from 36 to 109 in five steps — 36, 58, 79, 91 and 109 — with three darts per finish and a double to end on.
36 is a straight double: D18. If the dart lands in the single by mistake you are left on 18, which still has a double finish with the darts you have left. 58 is a two-dart finish: 18 D20.
79 is a two-dart finish: T13 D20. 91 is a two-dart finish: T17 D20. 109 needs all three darts: T17 18 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.