1. The problem asks to solve for $s$ in the equation $138 + s = 195$. 2. The formula used is to isolate $s$ by subtracting 138 from both sides: $$s = 195 - 138$$ 3. Perform the subtraction: $$s = 57$$ 4. Therefore, the solution is $s = 57$ km. This means the distance $s$ is 57 kilometers.