The average (arithmetic mean) cost per book for the \(12\) books on a certain table is \(k\) dollars. If a book that costs \(18\) dollars is removed from the table and replaced by a book that costs \(42\) dollars, then in terms of \(k,\) what will be the average cost per book, in dollars, for the books in the table?
A) \(k+2\)
B) \(k - 2\)
C) \(12+ \dfrac{24}{k}\)
D) \(12- \dfrac{24}{k}\)
E) \(12k-6\)
Answer: A
Source: GMAT Prep