x+4 Consider the function x} = 2 . X 7 Determine the number of points on the graph of y = x) that have a horizontal tangent line. In other words, determine the number of solutions to f'(x) = 0. :l Determine the values of x at which f(x) has a horizontal tangent line. Enter your answer as a comma-separated list of values. The order of the values does not matter. Enter DNE if x) does not have anyr horizontal tangent lines