The resultant e.m.f of the circuit is given by
ϵ=ϵ1−ϵ2
=10−5=5V
Also the resultant resistance of the circuit is given by,
Req=2.5+2.5+5+25+15
=50Ω
So, the current I through the circuit is given by,
I=VR=550=0.1A
As all the resistors are in series potential decreases among all of them according to their resistance, which is shown in figure
VA=0.25V,VB=4.25V
The potential difference between these two points will be,
V=VB−VA
=4.25−0.25
=4V