10 23 18 6 3 6 8 9 11 10 6 20 7 9 X 18 7 7 15 26 Cross a group, ask x should fill in what? What's the rule? --10 3-6-8 --7 --23 9-11-10 --7 --18 6-20-7 --15 --6 9-X-18 --26

3+6+8-7=10;9+11+10-7=23;6+20+7-15=18;
So x = 6 + 26-9-18 = 5

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