Answer:
21060
Step-by-step explanation:
Breaking down the summation into its component parts. noting
∑ 1 = n
∑n = [tex]\frac{1}{2}[/tex] n (n + 1), thus
∑(3n - 6) for n = 1 to n = 120
= 3∑n - 6∑1
= 3 × [tex]\frac{1}{2}[/tex] × 120 × 121 - 6 × 120
= 21780 - 720
= 21060
