Answer:
3n² + 8n
Explanation:
∑ (5 + 6r )
= ∑ 5 + 6 ∑ r
= 5n + 6 × n(n + 1)
= 5n + 3n(n + 1)
= 5n + 3n² + 3n
= 3n² + 8n
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