(1) x=3⋅9+1⋅13+1=7x = \dfrac{3 \cdot 9 + 1 \cdot 1}{3 + 1} = 7x=3+13⋅9+1⋅1=7 (2) x=3⋅9−7⋅13−7=−5x = \dfrac{3 \cdot 9 - 7 \cdot 1}{3 - 7} = -5x=3−73⋅9−7⋅1=−5 (3) x=5⋅9−1⋅15−1=11x = \dfrac{5 \cdot 9 - 1 \cdot 1}{5 - 1} = 11x=5−15⋅9−1⋅1=11 (4) x=9+12=5x = \dfrac{9 + 1}{2} = 5x=29+1=5