Fill in the blank: If you have any problems finding things, just ask Roger. He is very ____________ and will tell you where to find what you want.

Choosing "helpful" correctly fills the blank in the sentence because it is the appropriate adjective to describe someone who is willing and able to assist others. The context indicates that Roger has the capacity to provide support or guidance, which is exactly what "helpful" conveys.

The other words do not fit grammatically or contextually. "Unhelpful" would imply that Roger is not willing to assist, which contradicts the positive tone of the sentence. "Help" is a noun and does not function appropriately in this context, as the sentence requires an adjective to describe Roger's character. "Helped" is the past tense of the verb "help," and again, it does not suit the context of describing someone's ongoing ability to assist. Thus, "helpful" is the only choice that accurately captures the intended meaning in the sentence.