The Cham also requested Ming China to intervene by helping bring the Vietnamese back in line by force and demarcate the border between Champa and Vietnam. China, however, only verbally rebuked the Vietnamese for its incursion, which the Vietnamese ignored, proceeding with its attack and plan to destroy its rival. The Vietnamese then carried out its campaign. On November 28, 1470, Le Thanh Tong formally launched his attack as a 100,000-strong Vietnamese naval expedition set out that day, followed by another Vietnamese army consisting of 150,000 men on December 8. The Vietnamese army was reorganized to copy the Chinese army, armed with gunpowder weapons. Le Thanh Tong raised a total of 300,000-strong army in the battlefied and, significantly outnumbering the 100,000-strong Cham army. This came at a massive financial cost since it drained the Vietnamese treasury of 1,000 gold liang each day. However, it decisively won the war.
Question: After formally launching an attack, how many days later did Le Thanh Tong increase his army?
Answer: 10