Arithmetic sequences have the same value added repeatedly. There are 17 increments between a1 and a18 and the value changes a total of 102 (95 - -7). 102 divided by 17 shows that the value of 6 is being added each time. The 35th term is then given by a1+(35-1)*6 = -7 + 34*6 = -7 + 204 = 197.
