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Combinatorics Difficulty 2.0 Junior Find the answer United Kingdom

A rectangular chocolate bar is made of equal squares. Irena breaks off two complete strips of squares and eats the 12 squares she obtains. Later, Jack breaks off one complete strip of squares from the same bar and eats the 9 squares he obtains. How many squares of chocolate are left in the bar?

(A) $72$ (B) $63$ (C) $54$ (D) $45$ (E) $36$

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