Final answer:
Thalia's habit of counting backward to combat insomnia is supported by the drive theory of motivation as it helps achieve homeostasis by enabling her to sleep.
Step-by-step explanation:
According to drive theory of motivation, Thalia's habit of counting backward to fall asleep and alleviate her insomnia is a behavior that is homeostatically regulating her sleep. When suffering from insomnia, her physiological need for sleep creates a psychological drive to engage in behaviors that will help her attain homeostasis. The act of counting backward facilitates the onset of sleep, restoring balance, and as a result, the behavior is reinforced and becomes a recurring habit as it successfully reduces the drive for sleep.