Billing rate NCARB practice exam question

This question is taken from NCARB’s free project management practice exam.

Question 23
An architect planned 1,000 hours for the design development (DD) phase of a project with an average billing rate of $50 per hour. The project has a planned multiplier of 3.05 and a total DD phase compensation of 152,500. At the end of DD, the architect finds that an excess of 240 labor hours were needed for DD. What is the additional project cost? _______
Correct answer: 36600

CORRECT RESPONSE
$36,600
CALCULATION

  1. 240 (additional hours) x $50 (average hourly rate) x 3.05 (multiplier) = $36,600 in additional project costs

Section: Resource Management

I thought net multiplier is built into billing rate? So why would you multiply by 3.05? Thanks!