$$\frac{{20 + 8 \times 0.5}}{{20 - ?}}{\text{ = 12}}$$     Find the value in place of (?)

Let the missing number is x
$$\eqalign{ & {\text{Given,}} \cr & \frac{{20 + 8 \times 0.5}}{{20 - x}}{\text{ = 12}} \cr & \Rightarrow \frac{{20 + 4}}{{20 - x}} = 12 \cr & \Rightarrow \frac{{24}}{{20 - x}} = 12 \cr & \Rightarrow 20 - x = \frac{{24}}{{12}} = 2 \cr & \Rightarrow x = 20 - 2 \cr & \,\,\,\,\,\,\,\,\,\,\,\, = 18 \cr & {\text{Hence, the number is 18}} \cr} $$