HELP Calculating contact angle of benzene.

[Saterial]

Homework Statement

In an experiment to determine how well benzene wets glass, benzene was found to rise to 1.71 mm in a certain capillary tube at 20.0 C. In the same tube, water rose 4.90 mm at 20.0 C. Calculate the contact angle for benzene, give that at 20.0 C, benzene = 0.879 gcm^-3, pwater = 0.998 gcm^-3, benzene = 2.89 * 10^-2 Nm^-1 and ywater = 7.28 * 10^-2 Nm^-1. The contact angle for water is assumed to be theta = 0.

Homework Equations

y₁ = cosθ + y_1,2 - y₂ = 0

The Attempt at a Solution

I don't know where to start. I know y₁ can be found by finding the capillary radius of water and using that for benzene. But how do you find y_1,2 and y₂? Aren't they surface tensions of the solid glass surface which is not given?

 

[Borek]

At first glance, and without working it on paper - can't you calculate them from the information about water?