Five numbers, three darts each, doubles only to finish: ladder #251 asks for 34, 60, 79, 100 and 106.
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. 60 is a two-dart finish: 20 D20.
79 is a two-dart finish: T13 D20. 100 is a two-dart finish: T20 D20. 106 needs all three darts: T17 15 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.