What is the gasoline-air surface tension its height in the capillary tube is 0.4mm and the density of gasoline is 700 kg/m^3?

The rise of the gasoline in a capillary tube is given by
the relation:

h = (2*Sf*cos T)/(rho*g*r), where h is the
height of the gasoline column, Sf is the gasoline-air surface tension, T is the contact
angle, rho is the density of gasoline, g is the acceleration due to gravity and r is the
radius of the capillary tube.

You have only provided the
height of the liquid column and the density of the gasoline. It is not possible to
proceed further without knowing the radius of the capillary tube and the contact angle
as the height depends on it. For a broad capillary tube the height would be negligible
whereas it would be substantial if the capillary tube is made
narrow.

All I can provide from the information provided is
that the value of Sf that you require is given by Sf = h*rho*g*r/ 2*cos
T.

Here g is 9.8 m/s^2 and you know rho and h, substitute r
and T and you can determine Sf.