Kirchoff Voltage Law

   ∑    Vij=  0
loop

sum of voltage around any loop is 0

V7 + V1 + V5 + V6 =0
10 + ( -5 ) + (-2.5) + ( -2.5 ) = 0

V7 + V1 + v2 + V4 = 0
10 + ( -5 ) + (-2.5) + ( -2.5 ) = 0

 

I added V8 from V2 to V4 nodes.   We find they are in series since RTOTAL = R1 + R2

V8 = V2 + V4
-5 = (-2.5) + (-2.5)