\(\mathrm{i}=0.5 \mathrm{A}\)
\(\mathrm{E}_{2}=\mathrm{E}-\mathrm{ir}\)
\(=10-0.5 \times 5\) \(=7.5 \mathrm{V}\)
\(\mathrm{E}_{\mathrm{net}}=\mathrm{E}_{1}+\mathrm{E}_{2}=7.5 \mathrm{V}\)
\(\mathrm{i}=\mathrm{i}_{1}+\mathrm{i}_{2}\)
\(0.5=\frac{7.5}{x}+\frac{7.5}{30}\)
\(\mathrm{x}=30 \Omega\)