Five numbers, three darts each, doubles only to finish: ladder #257 asks for 22, 45, 77, 85 and 126.
22 is a straight double: D11. 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.
77 is a two-dart finish: T19 D10. 85 is a two-dart finish: T15 D20. 126 needs all three darts: T17 T17 D12. 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.