PROBLEM $60$

If $r$ is used to stand for the rate of change for a vertical curve and $x$ for the distance from the point of tangency, which of the following expressions would yield the tangent offset for any station along the curve?

$($A$)(\frac{r}{2})x^2$

$($B$)rx$

$($C$)r^2(\frac{x}{2})$

$($D$)\frac{2r}{x}$

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