If the sight distance (S) is equal to the length of the vertical-curve (2l) joining two grades g₁% and - g₂%, the height of the apex will be

ANS:B -

The formula is s(g1% - g2%)/200(√h1 + √h2)^2.
S= minimum sight distance.
g = gradient.
h1 = height of driver.
h2= height of the obstruction.

S = (√h1 +√h2) = 2l.
= 2l(g1% - g2%)/200(2l)^2.
= (g1% - g2%)/400 l. The Main formula.

L={(g1% -g2%)S^2}/(800 h).
But in this question.
Length of the vertical curve (L)=2l.
And, S=2l.

Then
h = {(g1% -g2%)(2l)^2}/(800 * 2l).
h = {(g1% -g2%)l}/400.