By increasing in temperature, the steel expanded from 85 meters to S meters. Finding S given this increase in temperature is a physics problem. But here is the math:
Suppose the track follows the curve of a circle of radius R, and central angle between the fixed point of the rail and the midpoint of the rail is . Then S/2=R . Similarly, . Solving this system of equations gives you all the information you need to find X. The vertical distance D between the ground and the center of the circle is and .
Say for example, the rail expanded from 85m to 90m. Then the solution to is . So the radius of the circle is 77.28m and the distance from the circle's center to the ground is 64.55m. Thus, the rail is sitting 12.72m off the ground. (Obviously, a realistic value of its expansion of a few millimeters will cause it to rise only a few centimeters.)