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$$2 q^{2}-q r-3 r^{2} \div 2 q^{2}-9 q r+9 r^{2}$$$\newline$$(q+r)(q+3 r)$$\newline$Cannot be simplified$\newline$$(a+r)(a-3 r)$$\newline$$(a-r)(a+3 r)$