Having trouble finding the voltage
Here's what you should do:


Calculate the voltage at node A, given the current through \$R_2\$ is known
Having the voltage at node A, find the current through \$R_3\$
Find the current through \$R_1\$ by applying KCL at node A
Now use KVL to figure out \$V_S\$


Throughout all of this stick to one convention for current/voltage sign for resistors and voltage sources. For example, here's one convention that people usually use: