Two coils connected in series have resistances $600 \mathrm{\Omega }$ and $300 \mathrm{\Omega }$ at $20 °\mathrm{C}$ and temperature coefficient of resistivity $0.001 {\mathrm{K}}^{-1}$ and $0.004 {\mathrm{K}}^{-1}$, respectively. The resistance of the combination at temperature $50 °\mathrm{C}$ is

Find equivalent resistance between point $X$ and $Y$.

Find equivalent resistance between $X$ and $Y$.

Find equivalent resistance between $X$ and $Y$.

Equivalent resistance between $X$ and $Y$.

Find equivalent resistance between $X$ and $Y$.