There's definitely something missing. These questions are supposed to practice trial and error -- I know because I am in the same type of class -- but to practice that, there has to be prices of the silk butterflies and silk roses so you can play around with numbers to solve for it.
Or maybe you just need to play with numbers like this:
Two silk butterflies, means two of the same number must be added together + 1 silk rose, a different or same number = $18
That could mean butterflies are 8 dollars each and roses are 2 dollars each since 8+8+2= 18
Or 7+7+3 = 18
And so on...
But it could also be each item is 6 dollars each since 6+6+6 = 18
But that would be a pretty weird question because you can answer it in so many ways, so shes either missing information or going for creative answers.
I hope this helps a little bit. Good luck!