Let 
be the distance from the left wall to the laser source and 
the distance form the right wall to the laser source.
We can use the cosine trigonometric function in the smaller triangle to relate the adjacent side of the angle and the hypotenuse; then we can solve for:
We can use the tangent trigonometric function in the larger triangle to relate the opposite side of the angle and its adjacent side; then we can solve for:
Now we can add both distances:
We can conclude that <span>the distance between the walls is 100 m.</span>
We can use the cosine trigonometric function in the smaller triangle to relate the adjacent side of the angle and the hypotenuse; then we can solve for
We can use the tangent trigonometric function in the larger triangle to relate the opposite side of the angle and its adjacent side; then we can solve for
Now we can add both distances:
We can conclude that <span>the distance between the walls is 100 m.</span>