Please answer the following questions in detail, provide in-text citations in support of your argument.

• Define the concept of stationarity time series and methods of removing non-stationarity
• The following data shows the coded sales of company X in successive 4-week periods over 1995-1998.

I II III IV V VI VII VIII IX X XI XII XIII 1995 153 189 221 215 302 223 201 173 121 106 86 87 108 1996 133 177 241 228 283 255 238 164 128 108 87 74 95 1997 145 200 187 201 292 220 233 172 119 81 65 76 74 1998 111 170 243 178 248 202 163 139 120 96 95 53 94