accounting 2 questions only

Here are the 2 homework questions. The second one should be a strong paragraph with a cited reference.

1.EXERCISE 3–10 Applying Overhead; Computing Unit Product Cost [LO2, LO3] 

A company assigns overhead cost to completed jobs on the basis of 120% of direct labor cost. The job cost sheet for Job 413 shows that $12,000 in direct materials has been used on the job and that $8,000 in direct labor cost has been incurred. A total of 200 units were produced in Job 413.

Required: 

What is the total manufacturing cost assigned to Job 413? What is the unit product cost for Job 413?

(check figure unit production cost 148)

2.Why do companies use a predetermined overhead rate rather than actual overhead costs to apply overhead to jobs?