Where am I wrong on showing the part f is decreasing?

Results for this submission Entered Answer Preview Result Message (0, 2.25) correct (-infinity, 0), (2.25, infinity) ( 00 ' ) . (0: 30-) 50% correct Your first interval, set or union is incorrect 2.25 correct None None correct At least one of the answers above is NOT correct. (1 point) Let f (xx) = 6\\x - 2x for x > 0. Find the open intervals on which f is increasing (decreasing). Then determine the x-coordinates of all relative maxima (minima). f is increasing on the intervals (0,9/4) f is decreasing on the intervals (-infinity,0), (9/4,infinity) 3. The relative maxima of f occur at x = 4. The relative minima of f occur at X = None Notes: In the first two, your answer should either be a single interval, such as (0,1), a comma separated list of intervals, such as (-inf, 2), (3,4), or the word "none". In the last two, your answer should be a comma separated list of x values or the word "none"