Puzzle: here's the product, what is the sum

The following is a question from the 2005 Australian Mathematics Competition - Junior Division (years 7 & 8):

In the multiplication

P Q R
x 3
------
Q Q Q

each of P, Q and R represents a different digit. The sum of P, Q and R is
(A) 16 (B) 14 (C) 13 (D) 12 (E) 10

If you know the answer, send it with an explanation to eliasblog@yahoo.com.au

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