For the second derivative I get -174/(3x-2)^3 which does not have an answer for equaling zero. my random guess doesn't work, DNE doesn't work if I use 0 for x I get -87/4 which also did not work. How do I do this?

Determine the open intervals on which the graph is concave upward or concave downward. [Enter your answers using interval notation. If an answer does not exist, enter DNE.) x 9 x = _ } 3x + 2 concave upward ('00... 0) X concave downward (0', 00) X