Respuesta :

when n = 1  first term  = -6 
n = 2  second term =  0
n = 3 third term = 6

n = 4 4th term = 12

so we have an Arithmetic sequence  first term = -6 and common difference = 6

Sum 14 terms  =  (14/2)[2*-6 + (14-1)*6]

 =  462  answer