Write the Word or Phrase That Best Completes Each Statement $f ( x ) = 37.8 e ^ { 0.18 x }$

Multiple Choice

Write the word or phrase that best completes each statement or answers the question.
-Suppose the number of Quickie hamburgers (in millions) served yearly can be modeled by $f ( x ) = 37.8 e ^ { 0.18 x }$ . Approximate how many years it takes for the number of hamburgers served to reach 77 million. Round to the nearest year.

A) $6 \mathrm { yr }$
B) $3 \mathrm { yr }$
C) $5 \mathrm { yr }$
D) $4 \mathrm { yr }$