what's the voltage across F
This is what I'm getting.
Maybe it's a typo ?

Loop 1:
-Ve + Va + Vb = 0;
Isolate Vb
Vb = Ve – Va;
20-10 = 10 =&gt; Vb = 10;
Loop 2:
-Vb – Vc – Vd = 0;
Isolate Vd
-Vd = Vb + Vc;
10+15 = -25;
Vf + Vd = 0
Vf = -Vd =&gt; Vf = 25;