Question

What is the adverb clause on Darla set up a studio because she enjoyed painting

Answer 1

Darla set up a studio because she enjoyed painting. This is an adverb clause because the 'because' in the sentence explains why Darla set up a studio.

Answer 2

The adverb clause in this sentence is because she enjoyed painting.
Adverb clauses behave as simple adverbs - they answer the questions such as "when," "where," "why," etc. So, this is no different.
Why did Darla set up a studio? Because she enjoyed painting.