Correct : 0.525 m

This is a highway engineering problem involving the calculation of super-elevation — the transverse banking of a road on a curve — as per IRC: 73-1980 for plain terrain.
The formula for super-elevation as per IRC is:
e = V² / (225 × R)
where V is the design speed in kmph and R is the radius of the curve in metres. Substituting the given values:
e = (100)² / (225 × 510) = 10000 / 114750 ≈ 0.0871
Now, as per IRC standards for plain and rolling terrain, the maximum permissible super-elevation is 0.07 (7%). Since our calculated value of 0.0871 exceeds this limit, we cap it at e = 0.07.
The level difference between the inner and outer edges of the road is simply the super-elevation multiplied by the total road width:
Level difference = e × Width = 0.07 × 7.5 = 0.525 m