Hello there,
So what we need to find how many number of costumes that can be made using ONLY 11

.
The first thing we would do is

÷
11

.
Your answer this this would be

.
To recheck this. . . We do

x

. . .
Your answer would be 11
.
That is how you recheck your work.
Your correct answer would be

Hope this helps! :)