Chapter 11 - Further Topics in Algebra - 11.2 Arithmetic Sequences and Series - 11.2 Exercises - Page 1026: 71

$-657$

$\sum ^{12}_{i=4}\left( -5-8i\right) =\dfrac {n}{2}\times \left( a_{4}+a_{12}\right) \Rightarrow a_{4}=-5-8\times 4=-45;a_{12}=-5-8\times 12=-101\Rightarrow S=\dfrac {9\times \left( -45+\left( -101\right) \right) }{2}=-657$