Problem $3(25$ points$)-$ For the circuit shown, the voltage at one node is known to be $10$ V as shown.

a$)$ Find the voltage at node Vy$.$

b$)$ Use resistor combinations to determine the equivalent resistance between the $10$ V node and ground.

c$)$ Find the source voltage, Vx$.$

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Problem $4(30$ points$)-$ For the circuit shown, find the Thevenin equivalent for the circuit at the left of terminals a$-$b$.$

a$)$ Find the open circuit voltage, Voc, at terminals a$-$b$.$

b$)$ Find the Thevenin equivalent resistance, Rth$,$ at terminals a$-$b$.$

c$)$ Show the Thevenin equivalent circuit with the rest of the circuit $($R$3$ and R$4)$ connected.

d$)$ Find Vx$.$