The Chinese were solving 14th degree polynomials in 1303, why?


Reading through the wikipedia on Chinese Mathematics, I came across a myriad of surprises including:

“Si-yüan yü-jian (《四元玉鑒》), or Jade Mirror of the Four Unknowns, was written by Zhu Shijie in 1303 AD and marks the peak in the development of Chinese algebra. The four elements, called heaven, earth, man and matter, represented the four unknown quantities in his algebraic equations. It deals with simultaneous equations and with equations of degrees as high as fourteen.”

A main takeaway I get from this article is that Chinese mathematics was not motivated by the beauty of mathematics or its theory (most things were left unproven), but by purely practical concerns of astronomy and engineering. What practical problem warranted a 14th degree equation?