Manipur was a tributary to Burma in the 16th century  but had gone its own way since. It raided Upper Chindwin region in 1647 and 1692. However, in 1704, the raja of Manipur presented his daughter to Ava. Starting in the 1720s, Manipur under the leadership of Pamheiba  became a thorn to Upper Burma. In early 1724, the Manipuris raided Upper Burma. In response, an expedition force of 3,000 men marched to Manipur in November 1724. The army was ambushed in the swamps at Heirok, and retreated in haste. The Manipuris then returned ten years later. From 1735 to 1741, Manipuris raided the Upper Chindwin regions, increasingly deeper with each raid. Burmese defences were simply bypassed the Manipuris on their horseback. In December 1739, they reached as far as Sagaing, and looted and burned everything insight. The Burmese defences finally stopped them at Myedu in early 1741, with each side agreeing to an uneasy truce. But the Manipuris had annexed the Kabaw valley. The truce did not last. Another raid came all the way down to Ava in 1744. The last raid came in 1749. Upon arrival at Ava, the Manipuri chief found a large Burmese army, and presented his 12-year-old daughter instead, and left.
Question: How many years did Manipuris raid the Upper Chindwin regions?
Answer: 6