I believe this can be modeled by the equation:
w=120+5(h-30)
Tang Dynasty was able to strengthen China thru the efforts of its Tang Taizong and Empress Wu in which the former brought back China's government and the latter empowered women. The Song dynasty continued the good governance and elevated the military system thru systematized testing.
What was the Open Door policy? The Open Door policy was a statement of principles initiated by the United States in 1899 and 1900. It called for protection of equal privileges for all countries trading with China and for the support of Chinese territorial and administrative integrity.
1 trillion is 10x larger than 1 billion.