\(\Leftrightarrow\left(\dfrac{3}{2}\right)^x=\left(\dfrac{3}{2}\right)^{20}:\left(\dfrac{3}{2}\right)^4=\left(\dfrac{3}{2}\right)^{16}\)
=>x=16
\(\dfrac{81}{16}\cdot\left(\dfrac{3}{2}\right)^x=\left(-\dfrac{3}{2}\right)^{20}\)
\(\left(\dfrac{3}{2}\right)^4\cdot\left(\dfrac{3}{2}\right)^x=\left(\dfrac{3}{2}\right)^{20}\)
\(\left(\dfrac{3}{2}\right)^x=\left(\dfrac{3}{2}\right)^{20}:\left(\dfrac{3}{2}\right)^4\)
\(\left(\dfrac{3}{2}\right)^x=\left(\dfrac{3}{2}\right)^{\left(20-4=16\right)}\)
`=>x=16`