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Series basics challenge

Evaluate:   k=18(4k2+6k)~~\displaystyle\sum\limits_{k=1}^{8}{\left(-4 k^2+6k \right)}\,.
  • Your answer should be
  • an integer, like 66
  • an exact decimal, like 0.750.75
  • a simplified proper fraction, like 3/53/5
  • a simplified improper fraction, like 7/47/4
  • a mixed number, like 1 3/41\ 3/4
For reference:
i=1ni2=n(n+1)(2n+1)6\qquad\displaystyle\sum\limits_{i=1}^{n}{i^2=\frac{n\left( n+1 \right)(2n+1)}{6}}
i=1ni=n(n+1)2\qquad\displaystyle\sum\limits_{i=1}^{n}{i=\frac{n\left( n+1 \right)}{2}}