\(0.5 = \frac{E}{{2 + r}}\) ...... \((i)\)
\(0.25 = \frac{E}{{5 + r}}\) ..... \((ii)\)
Dividing \((i)\) by \((ii)\),
we get \(2 = \frac{{5 + r}}{{2 + r}}\) \( \Rightarrow \) \(r = 1\,\Omega \)
\(0.5 = \frac{E}{{2 + 1}}\) \( \Rightarrow \) \(E = 1.5\,V\)