$\begin{array}{l}\text{Here, put x at the place of ?}\\ \\ i.e,\frac{x^{0.8}}{49}=\frac{189}{{?}^{2.2}}\\ \\ =x^{0.8+2.2}=189\times 49\\ \\ \text{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}[add the power in multiplication]}\\ \\ \Rightarrow x^3=189\times 49\\ \\ =\frac{27\times 7\times 49}{3\times 3\times 3\times 7\times 7\times 7}\\ \\ \Rightarrow x=3\times 7=21\end{array}$