i need your help regarding sum if. I have bulk data in which we have recorded customer count per hour and i want to sum the count in two different date range. i.e

Date Hr1 Hr2 Hr3 Hr4 Hr5 Hr6 Hr7 Hr8 Hr9
13-08-01 226 239 94 25 60 82 68 70
13-08-02 211 178 74 14 76 86 89 73
13-08-03 220 167 71 23 80 84 97 73
13-08-04 210 187 141 21 78 79 76 61
13-08-05 237 210 141 11 7 65 87 72 57
13-08-06 255 233 150 12 19 109 102 82 79
13-08-07 388 332 276 121 12 81 93 86 90
13-08-08 221 166 143 23 68 225 240 179
13-08-09 191 184 146 6 24 119 191 244 147
13-08-10 231 151 113 6 41 99 165 216 189


please help how to sum.