Explanation : As you can see, [tex]\sqrt{-16}[/tex] is not a real number, and hence should be expressed as 4[tex]i[/tex], [tex]i[/tex] being an imaginary number. Respectively [tex]\sqrt{-64}[/tex] will be 8[tex]i[/tex]. Therefore this expression boils down to [tex]\left(3+4i\right)\left(6-8i\right)[/tex]. All we have to do from now on is expand this expression.
Apply the rule [tex]\left(a+bi\right)\left(c+di\right)=\left(ac-bd\right)+\left(ad+bc\right)i[/tex], in this case where [tex]a=3,\:b=4,\:c=6,\:d=-8[/tex],
[tex]\left(3\cdot \:6-4\left(-8\right)\right)+\left(3\left(-8\right)+4\cdot \:6\right)i[/tex]
Let's simplify each part, [tex]3\cdot \:6-4\left(-8\right)[/tex] and [tex]3\left(-8\right)+4\cdot \:6[/tex]. Afterwards we can add [tex]i[/tex], and refine.
[tex]3\cdot \:6-4\left(-8\right) = 50[/tex] ; [tex]3\left(-8\right)+4\cdot \:6 = 0[/tex]
Therefore our simplified expression will be [tex]50+0i[/tex], otherwise known as just 50. That is our solution.
