I think it would be helpful in this case to know more about this exercise. You have included only the exxample. What about the rest of the exercise items? Do they also have proofreading marks? It looks like the purpose of this exercise is for the student to apply proofreading marks to sentences or not, depending on whether they are identified as correct. Is there a list of proofreading marks given in the adjacent text? Consider what it says in Section 6c--Proofreading marks are of no practical value to the braille reader. If the purpose of this exercise is only to identify incorrect sentences and to correct them, braille readers will not be doing that by applying proofreading marks. Therefore, it might be appropriate simply to give this example in corrected and uncorrected even though there are no transpositions. You'll have to decide based on the surrounding text, which was not included.