Five numbers, three darts each, doubles only to finish: ladder #242 asks for 36, 54, 66, 86 and 120.
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. 54 is a two-dart finish: 14 D20.
66 is a two-dart finish: T18 D6. 86 is a two-dart finish: T18 D16. 120 needs all three darts: T20 20 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 last finish is long. Throw the first dart at the big treble with intent, then let the board work out what is left.