Answer
a) No
b) See the figure below.
Work Step by Step
a) To make sure if the motion of the object is at a constant acceleration or not, we need to use the three kinematic formulas to see if all of them are giving the same value of $a_x$ or not. If all the 3 equations give us the same result, then the acceleration is uniform, and if not then the acceleration is not uniform.
$$v_{fx}=v_{ix}+a_x\Delta t$$
Solving for $a_x$;
$$a_x=\dfrac{v_{fx}-v_{ix}}{t_f-t_i}=\dfrac{11-0}{5-0}=\bf 2.2\;\rm m/s^2$$
$$v_{fx}^2=v_{ix}^2+2a_x\Delta x$$
Solving for $a_x$;
$$a_x=\dfrac{v_{fx}^2-v_{ix}^2}{2(x_f-x_i)}=\dfrac{11^2-0}{2(40-0)}=\bf 1.51\;\rm m/s^2$$
Since these two results are not the same, the acceleration is indeed not uniform and we do not have to test the third kinematic formula.
b)
We only have two dots of data which are
$\rm (0\;t,0\;m/s)$ and $\rm (5\;t,11\;m/s)$
We also know that the area under the curve must equal the distance traveled by the object which is 40 m.
So, we need to find a suitable shape for these two points that make the area under the curve equal to 40 m.
We can see that when the curve is a straight line (which fits if the acceleration was uniform) that the area is less than 40 m.
And hence if the curve is concave up, then the area under the curve decreases.
Therefore, the only way for this curve is to be concave down.
See the figure below and note that the suitable curve is the blue one (not the red or the black).
