Five numbers, three darts each, doubles only to finish: ladder #221 asks for 4, 46, 64, 99 and 105.
4 is a straight double: D2. If the dart lands in the single by mistake you are left on 2, which still has a double finish with the darts you have left. 46 is a two-dart finish: 6 D20.
64 is a two-dart finish: T8 D20. 99 needs all three darts: T17 8 D20. If the first dart misses its treble, the board will show the new route straight away. 105 needs all three darts: T17 14 D20. If the first dart misses its treble, the board will show the new route straight away.
At best the five finishes need 11 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.