Complex sentence: Both versions were available to pre-order in the United States on September 25; the 7 inch WiFi model was released on October 18, while the 8.9 inch WiFi model was released on November 7,2013.
Split into simpler sentences: Both versions were available to pre-order in the United States on September 25 2013. A 7 inch WiFi model was released on October 18, while an 8.9 inch WiFi model was released on November 7,2013.