Explanation:
2a + 2b + 2c
= (a + b) + (b + c) + (c + a)
= 5 + 6 + 7
= 18.
Hence, a + b + c = 9 and a = (a + b + c) - (b + c) = 9 - 6 = 3.
Answer:
a = 3
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