Answer
a) $x=\pm 2$
b) No.
Work Step by Step
$$\color{blue}{\bf [a]}$$
The probability density is maximum when the number of dots per unit length is greatest, and is minimum when the number of dots per unit length is smallest.
From the given figure, we can see that the number of dots per unit length is greatest at $x=\pm 2$
$$\color{blue}{\bf [b]}$$
No, we cannot determine this, as the probability density is given by the absolute square of the wave function.
