UKMT Grey Kangaroo, 2015

Algebra Difficulty 2.0 Junior Find the answer United Kingdom

Ria wants to write a number in each of the seven bounded regions in the diagram. Two regions are neighbours if they share part of their boundary. The number in each region is to be the sum of the numbers in all of its neighbours. Ria has already written in two of the numbers, as shown. What number must she write in the central region?

(A) $0$ (B) $1$ (C) $-2$ (D) $-4$ (E) $6$

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