LEFT and Reena is seventeenth from the right.Since Shilpa and Reena interchange positions, so Shilpa's NEW position is the same as Reena's earlier position.So, this position is 14th from the left and 17th from the right.Therefore, TOTAL number of girls in the row = 14 + 17 - 1= 31 - 1= 30 Hence, '30' is the correct answer.