A pair solved by elimination

You will write a function that solves a pair of equations by elimination, and one that checks an answer in both equations.

Your tasks.

1. In solve_elim, return (x, y) for $a_1x + b_1y = c_1$ and $a_2x + b_2y = c_2$. Use $d = a_1b_2 - a_2b_1$, $x = \dfrac{c_1b_2 - c_2b_1}{d}$ and $y = \dfrac{a_1c_2 - a_2c_1}{d}$. If $d$ is $0$, return None.
2. In holds, return True when (x, y) satisfies both equations, and False when it does not.
3. Set answer to the solution of $7x + 3y = 31$ and $2x - 5y = 3$, using your function.