We know that,
Number of scouts = 15
Number of feathers required by each scout = 18
Hence, Total Number of feathers required = 15 * 18 = 270
We also know that Number of feathers in each bag = 12
Hence, number of bags required to decorate picture frames = Total number of feathers required ÷ number of feathers in each bag
⇒ Number of bags required to decorate picture frames = 270 ÷ 12
⇒ Number of bags required to decorate picture frames = 22.5
Since half a bag can't be bought 23 bags would be required.