The correct answer is A. 6155 mm2.
The cross-sectional area of a rail is the area of the shape that is formed by the top and bottom of the rail, as well as the two sides of the rail. The cross-sectional area of a rail is important because it determines the strength of the rail. A rail with a larger cross-sectional area is stronger than a rail with a smaller cross-sectional area.
The cross-sectional area of a 52 kg flat footed rail is 6155 mm2. This is because the cross-sectional area of a rail is calculated by multiplying the width of the rail by the height of the rail. The width of a 52 kg flat footed rail is 150 mm and the height of a 52 kg flat footed rail is 45 mm. Therefore, the cross-sectional area of a 52 kg flat footed rail is 6155 mm2.
The other options are incorrect because they do not represent the correct cross-sectional area of a 52 kg flat footed rail.