Finding Transfer Response (Simplifying resistor circuit)
You have at least three ways:


Use the general node voltage method and solve the voltage over RL.
Find the Thevenin equivalent for V1, R1, R2, R3 and R4. It's what RL sees. Then you get easily the voltage over RL by using the voltage divider equation.
You can remove one resistor if you transform R1,R2,R3 from delta to Y. R4 can be combined with the mid branch of the Y. The rest can be solved using series and parallel resistors equations and the voltage divider equation.


3 does not shorten the calculations. I would try 2 at first if the transfer function from V1 to the voltage over RL was the actually wanted thing.

Method 1 is the brute force way. You can form two equations having the voltages over R4 and RL as the unknowns.