GAUSS8 2015 Problem 21

Past Contests GAUSS8 GAUSS (GR. 8) - 2015
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1

In square PQRS,M is the midpoint of PS and N is the midpoint of SR. If the area of \triangle{SMN} is 18, then the area of \triangle{QMN} is

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Answer Choices
A. 36
B. 72
C. 90
D. 48
E. 54