Concave up is U-shaped.
There will be a inflection/critical point f'(x) =0 then a negative slope f'(x) = neg then another inflection/critical point f'(x) =0 at the bottom of the U-shape then a positive slope to last inflection/critical point. The interval for the Concave Up shape is the first and last inflection points.
The correct answer is 16/81. Hope this helps.
I hope this helps you
2x=5+1,3
2x=6,3
x=3,15
