Read the sentence.

It was not exactly what he had in mind when he agreed to do the task.

Which word is the adverb modifying another adverb?

The word not modifies the word exactly.

Explanation:

An abverb is a word (or phrase) that modifies a verb (or adjective, or even another adverb). When modifying a verb, an adverb basically says how something is done.

Adverbs often end in - ly. We can spot the word exactly, which is describing the action of having something in mind. The word not, which is also an adverb, modifies the word exactly because it changes something about the meaning of exactly.