$$\sqrt {\frac{{0.0196}}{?}} = 0.2$$

$$\eqalign{ & {\text{Let ,}} \cr & \sqrt {\frac{{0.0196}}{x}} = 0.2 \cr & {\text{Then,}} \cr & \Leftrightarrow \frac{{0.0196}}{x} = 0.04 \cr & \Leftrightarrow x = \frac{{0.0196}}{{0.04}} \cr & \Leftrightarrow x = \frac{{1.96}}{4} \cr & \Leftrightarrow x = 0.49 \cr} $$