Answer:
21060
Explanation:
Breaking down the summation into its component parts. noting
∑ 1 = n
∑n = n (n + 1), thus
∑(3n - 6) for n = 1 to n = 120
= 3∑n - 6∑1
= 3 × × 120 × 121 - 6 × 120
= 21780 - 720
= 21060
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n (n + 1), thus × 120 × 121 - 6 × 120