Final answer:
Sentences 5 and 6 most strongly suggest that this is an opinion/editorial column.
Step-by-step explanation:
The sentences that most strongly suggest that this is an opinion/editorial column are Sentences 5 and 6. Sentence 5 expresses the opinion that substituting art for graffiti might be a good thing in a metro area like Denver, while Sentence 6 mentions that the Englewood officials are prosecuting Mahaney for doing just that, which implies disagreement with his actions. These sentences reflect the writer's viewpoint on the subject and indicate that this is an editorial column.