Cost Accounting Standard Hours Question Need Help

Question

Hall Company's standards call for 900 direct labor hours to produce 500 units. During May 400 units were produced. The company worked 700 direct labor hours. The standard hours allowed for May's production would be ?
A) 900 B) 720 C) 480 D) 700 E) None
Answer was B) but I need help with steps as to how

Answer 1

It takes 900 hours to produce 500 units, so that is 1.8 hours per unit (900 / 500).  Therefore, if they produced 400 units in May, it would be 1.8 standard hours x 400 units = 720.