x+4 Consider the function F{x} = 2 . x + 9 Determine the number of points on the graph of y 2 x) that have a horizontal tangent line. In other words, determine the number of solutions to f'{x) = I). 1 3' Determine the values ofx at which {(x) has a horizontal tangent line. Enter your answer as a commaisepalated list of values. The order of the values does not matter. Enter DNE if for) does not have any horizontal tangent lines. 9 X