I'm not sure why you computed $P(\text{Positive | Disease})$. The question asks for $P(\text{No disease | Positive})$.
We have
$$\begin{align*} P(\text{No disease | Positive}) &=\frac{P(\text{No disease } \cap \text{ Positive})}{P(\text{Positive})}\\\\\\\ &=\frac{0.64\cdot0.07}{0.64\cdot0.07+0.36\cdot0.9}\\\\\\\ &\approx 0.1215 \end{align*}$$