6 7 2y 9 35 July 8, 2019 16 32 64 128 6 9-3 2×3 5 6 7×(7 9-y)=28 81 6 7 x- 5 9 y=2 - 2 21 x- 1 9 y=6 6 7/9 - 2 2/7 6 9 (-2 3)