Part A $-$ Find the open$-$circuit voltage

Express your answer with the appropriate units.

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Hint $1.$ How to approach this problem preliminary analysis will show you that one of these methods requires you to write and solve two equations, whereas the other requires you to write and solve three equations.

Hint $2.$ Using the node$-$voltage method bottom node is the open$-$circuit voltage, so once you have solved the two simultaneous equations you have found the open$-$circuit voltage.

Hint $3.$ Using the mesh$-$current method the voltage drop across the $40k$ resistor, which is the open$-$circuit voltage.