A right triangle is made, where lengths of the walls are the legs and the distance from the end of wall 1 to the end of wall 2 is the hypotenuse.
If there is a right angle, the Pythagorean theorem must be satisfied.
12² + 14² = 18²
144 + 196 = 324
340 ≠ 324
Then, the walls don't meet at a right angle.