`3\sqrt{75}-4\sqrt{48}+\sqrt{108}`
`=3\sqrt{5^2 .3}-4\sqrt{4^2 .3}+\sqrt{6^2 .3}`
`=15\sqrt{3}-16\sqrt{3}+6\sqrt{3}=5\sqrt{3}`
\(=3\cdot5\sqrt{3}-4\cdot4\sqrt{3}+6\sqrt{3}=15\sqrt{3}-16\sqrt{3}+6\sqrt{3}=5\sqrt{3}\)
\(A=15\sqrt{3}-16\sqrt{3}+6\sqrt{3}=5\sqrt{3}\)