"Assess" is the most appropriate synonym for "estimate" because both words involve making a judgment or approximation of the value, size, or extent of something. "Solve," "discover," and "believe" have different meanings and do not convey the idea of making an estimation or assessment.

The most appropriate synonym for "confusion" is "commotion." "Confusion" refers to a state of disorder or lack of clarity, and "commotion" reflects a similar state of tumult or disturbance. The other options, such as "intrepidity" (fearlessness), "stagnation" (lack of progress), and "perusal" (reading or examination), have different meanings and do not convey the sense of disorder associated with "confusion."