Thevenin Voltage Problem
Remove the 10Ω resistor;
Calculate the voltage at the nodes where the 10Ω resistor was connected;
Remove the voltage sources and calculate the equivalent resistance you see when you look into the circuit from the point where the 10Ω was connected.



   2.1. Calculate the current through the circuit;
 2.2. Calculate the voltage drop across one of the resistors;
 2.3. Calculate the node voltage.


This looks like homework, so I'm not writing down exact formula's, rather indications.

bullet 2. Gets you the Thevenin voltage, somewhere half way between 3 and 4 Volt
bullet 3. Gets you the Thevenin resistance, somewhere around 15Ω

Now you do the math and give us the formula's and exact numbers.