What is the sum of the geometric sequence -1, 6, -36, . . if there are 6 terms?

The formula  is  

Sn  = a1.  1 - r^n
                    where r = common ratio and a1 = first term
                 1 - r

Here we have r = -6  and a1 = -1, and n = 6. So:-

Sum of 6 terms S6  =  -1 *    1 - (-6)^6
                                           = 6665
                                            1 - (-6)

W-14=t. that i think is the answer idk