The customer service department for a large electronics store receives a significant number of phone calls each day. On an average business day, the department receives 162 calls in the first three hours they are open. After nine hours, they have received an average of 486 calls. Assuming the calls come in at a constant rate, which of the following applies? A. An additional hour is associated with an additional 108 phone calls. B. An additional hour is associated with an additional 36 phone calls. C. An additional hour is associated with an additional 54 phone calls. D. An additional hour is associated with an additional 72 phone calls.