b
The equivalent resistance of series combination

is \(R_{s}=R_{1}+R_{2}=300 \mathrm{W}+500 \mathrm{W}=800 \mathrm{W}\)

The error in equivalent resistance is given by

\(\Delta \mathrm{R}=\left(\Delta \mathrm{R}_{1}+\Delta \mathrm{R}_{2}\right)=(3+4) \mathrm{W}=7 \mathrm{W}\)

Hence, the equivalent resistance along with

error is \((800 \pm 7) \Omega\)