recall that we add the common difference to get the next term.
[tex] \bf \begin{array}{|c|l|ll}\cline{1-2}x&y\\\cline{1-2}1&16\\2&16+d\\3&16+d+d\\4&16+d+d+d\\&4\\\cline{1-2}\end{array}~\hspace{5em}16+3d=4\implies 3d=-12\\\\\\d=\cfrac{-12}{3}\implies d=-4\\\\[-0.35em]\rule{34em}{0.25pt}\\\\~\hfill \begin{array}{|c|c|ll}\cline{1-2}x&y\\\cline{1-2}1&16\\&\\2&\stackrel{16-4}{12}\\&\\3&\stackrel{12-4}{8}\\&\\4&\stackrel{8-4}{4}\\&\\5&\stackrel{4-4}{0}\\\cline{1-2}\end{array}~\hfill [/tex]
