According to given circuit diagram,
As we know that, parallel equivalent resistance,
=1R1+++... and series equivalent resistance,
Req=R1+R2+R3+... Let the net resistance across a and b be R’
∴=+ a=+= R' = 5 Ω
Hence, total resistance,
R=R′+1=5+1=6Ω According to current division rule, current in upper branch,
I1=I. =1.==.=×=1A Again, according to current division rule, current in 15Ω resistor
I15=I1.=1×=0.4A ∴ Voltage drop across15Ω resistor,
V15=I15×15=0.4×15=6V