`= (6 sqrt 15)/5 . 9 sqrt 10 . sqrt(16) . sqrt 6`.
`= (6 . sqrt 15 . 9 sqrt 10 . 4 . sqrt 6)`
`= (6 . sqrt 3 . 9 sqrt 2 . 4 . sqrt 6)`
`= 6^2 . 9 . 4 = 6^4 = 1296`.
\(\sqrt{21,6}.\sqrt{810}.\sqrt{11^2-5^2}=\dfrac{6\sqrt{15}}{5}.9\sqrt{10}.4\sqrt{6}=1296\)