What is an inference?
a. a statement by the author about the meaning of a work
b. a conclusion the reader makes based on information in a text
c. an observation based on instinct and intuition
d. a judgement made about the theme or message of a work?

The answer is letter b. a conclusion the reader makes based on information in a text.

Explanation:

Inference is the act or process of inferring, which means reaching a conclusion based on information you have. That information may be obtained through life experience, interaction with others, reading texts, the news etc. It will serve as evidence to support the reasoning that will lead to the conclusion. Inference is synonym to deduction, conclusion, and assumption.

The three parts that best support the view that the narrator equates the salesman with an evil entity  are:

"Impious wretch!" foamed the stranger, blackening in the face as the rainbow beamed

The scowl grew blacker on his face; the indigo-circles enlarged round his eyes as the storm-rings round the midnight moon. He sprang upon me.

I trod it; and dragging the dark lightning-king out of my door, flung his elbowed, copper scepter after him.

took the test and got it right :)