The confidence interval is: $\bigg(p^* - z_{\frac\alpha2}\cdot \sqrt{\dfrac{p^*\cdot (1-p^*)}{n}}, p^* + z_{\frac\alpha2}\cdot \sqrt{\dfrac{p^*\cdot (1 - p^*)}{n}}\bigg)$. Here $p^* = \dfrac{200}{700} = 0.286$, $1 - p^* = 0.714$, $n = 700$, $z_{\frac\alpha2} = 1.96$. So $C.I = (0.253, 0.319)$