the difference between -11 and -18 is -7
the difference between -18 and -25 is -7
the difference between -25 and -32 is -7
therefore we can say that the difference between all of the terms will be -7.
the first term is -11 -> call this a
the difference is -7 -> call this d
the number of terms is 14 -> call this n
use the equation (sum of)\(_{n}\) = \(\frac{n}{2}\)(2a + (n-1)d)
(sum of)\(_{n}\) = \(\frac{14}{2}\)(2 x -11 + (14-1)-7)
= -7(-22 + (13 x -7))
= -7(-22 + -91)
= -7(-111)
= 777
