Checkout ladder #250 climbs from 34 to 121 in five steps — 34, 46, 65, 87 and 121 — with three darts per finish and a double to end on.
34 is a straight double: D17. A miss into the single leaves an odd number, so the next dart has to set up a double before you can finish. 46 is a two-dart finish: 6 D20.
65 is a two-dart finish: T19 D4. 87 is a two-dart finish: T17 D18. 121 needs all three darts: T18 T17 D8. 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 last finish is long. Throw the first dart at the big treble with intent, then let the board work out what is left.