Answer
The direction of the third piece is an angle of $45^{\circ}$ above the +x axis.
Work Step by Step
In part (a), we found that the velocity of the third piece is $~~v = (10~\hat{i}+10~\hat{j})~m/s$
We can find the direction as an angle $\theta$ above the +x axis:
$tan~\theta = \frac{10~m/s}{10~m/s}$
$\theta = tan^{-1}~(\frac{10~m/s}{10~m/s})$
$\theta = 45^{\circ}$
The direction of the third piece is an angle of $45^{\circ}$ above the +x axis.
