Thevenin based question - Mesh circuit

[KK25]

Homework Statement

First post here... Sorry it has to be a question.

I'm currently studying electrical engineering at university. Anyway, I've hit a couple of these mesh type circuits in my workbook and have no idea how to tackle them?

The question asks to solve using Thevenin's Theorem, but they look completely different to our worked examples and I'm at a loss as to where to begin, let alone solve the questions!

Homework Equations

Here is one of the questions -

Given: E1 = 200 V;
R1 = 15 Ω; R2 = 20 Ω;
R3 = 20 Ω; R4 = 12 Ω
and RL = 27 Ω

(a) Use Thevinin’s theorem
to determine the value of
current I.

(b) Check you answer using
Δ-to-Y transformation
and Kirchhoff’s laws.

The Attempt at a Solution

Like I said, unfortunately I don't know where to begin with this

Thanks in advance to anyone who can help me out here.

 

[The Electrician]

Have a look at this:

http://kauko.hallikainen.org/rw/theory/theory6.html

 

[KK25]

Have a look at this:

http://kauko.hallikainen.org/rw/theory/theory6.html

Thanks very much for the reply and link. At least now I have some idea of what I'm looking at!

I'll try working through the points referring to the 'Loaded Unbalanced Bridge' and see what I can come up with. I'll post back with my attempt.

Thanks again