There are 1 questions in this calculation: for each question, the 4 derivative of n is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ 4th\ derivative\ of\ function\ (l - 1)(n - 1)\ with\ respect\ to\ n：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = ln - l - n + 1\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( ln - l - n + 1\right)}{dn}\\=&l + 0 - 1 + 0\\=&l - 1\\\\ &\color{blue}{The\ second\ derivative\ of\ function:} \\&\frac{d\left( l - 1\right)}{dn}\\=&0 + 0\\=&0\\\\ &\color{blue}{The\ third\ derivative\ of\ function:} \\&\frac{d\left( 0\right)}{dn}\\=&0\\\\ &\color{blue}{The\ 4th\ derivative\ of\ function:} \\&\frac{d\left( 0\right)}{dn}\\=&0\\ \end{split}\end{equation} \]

Your problem has not been solved here? Please take a look at the  hot problems ！