Lever rule, help needed asap

[abs123456]

Could someone please help me on this question. I do not really understand
how to use the lever rule.
Attactched is an example..
Thanks very much

[lifeson22]

Consider the homogeneous liquid at the eutectic composition (50% To an 50% Lb). When you cool it to room temperature, you get two distinct phases, alpha and beta.

By the lever rule, the relative concentration f alpha and beta phases is calculated as follows:

1. beta phase: ([Lb](eutectic)-[Lb](alpha))/([Lb](beta)-[Lb](alpha))
2. alpha phase: ([Lb](beta)-[Lb](eutectic))/([Lb](beta)-[Lb](alpha))

In other words the relative concentration of alpha phase is the length ratio of the eutectic-beta and alpha-beta lines; for beta phase, that is the length ratio of alpha-eutectic/alpha-beta lines.