9

8 x (7) = 56
7 x (6) = 42
6 x (5) = 30
5 x (4) = 20
3 x (3) = answer "9"

90


2x3=6, 3x4=12, 4x5=20, 5x6=30, 6x7=42, (missing 7x8=56, 8x9=72), 9x10=90

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