Answer
$1.06\;\rm N\cdot m^2/C$
Work Step by Step
We know that the electric flux is given by
$$ \Phi=\vec E\cdot \vec A\tag 1$$
We also know that the electric field is uniform over the given area and we know that the area vector is perpendicular to the $xz$-plane.
$$\vec A=\pi r^2\;\hat i \tag 2$$
Recall that $\hat k\cdot \hat k=1\times 1\times \cos 0^\circ=1$ and that $\hat i\cdot \hat k=\hat j\cdot \hat k=1\times 1\times \cos 90^\circ=0$
Plug $\vec E$ from the given formula and $\vec A$ from (2) into (1),
$$ \Phi=(1500\;\hat i+1500\;\hat j-1500\;\hat k)\cdot (\pi r ^2\;\hat i)= 1500\times \pi (1.5\times 10^{-2})^2 +0+0$$
$$\Phi=\color{red}{\bf 1.06}\;\rm N\cdot m^2/C$$
