Angles, distances and the meeting line

You will write three functions for two planes. They find the distance of a point from a plane, the acute angle between two planes and the line in which two planes meet. A plane is stored as $(A, B, C, k)$ for $Ax + By + Cz = k$.

The idea. The distance of $(x_1, y_1, z_1)$ from the plane is $\dfrac{\lvert Ax_1 + By_1 + Cz_1 - k \rvert}{\sqrt{A^2 + B^2 + C^2}}$. The angle has $\cos\theta = \dfrac{\lvert \vec{n}_1 \cdot \vec{n}_2 \rvert}{\lvert \vec{n}_1 \rvert \lvert \vec{n}_2 \rvert}$. The line has direction $\vec{n}_1 \times \vec{n}_2$, and a point of it comes from setting $z = 0$.

Your tasks.

1. Finish distance(plane, point).
2. Finish angle_between(plane1, plane2). Return the acute angle in degrees.
3. Finish meeting_line(plane1, plane2). Return a point with $z = 0$ and a direction, as two tuples. Solve the two equations for $x$ and $y$ with Cramer's rule.