clarify

solutions/silver/baltic-12-mobile.mdx

@@ -133,7 +133,7 @@ From here on, we'll refer to this point as $p(a, b)$, where $a$ and $b$ are stat
 
 Now, let's consider cases where there exist unnecessary stations.
 
-Without loss of generality, let's assume all points are above the y-axis, and $a_x < b_x < c_x$.
+Without loss of generality, let's assume all points are above the y-axis, and $a_x < b_x < c_x$. If not all the points are above the y-axis, we can just flip their sign because the distance to the x-axis remains the same.  
 
 ### Case 1: $p(a, b) < p(b, c)$