The value of 28 + 10 3 - 7 - 4 3 is closest to:

Answer: Option D

$$\begin{array}{rl}& \sqrt{28+10\sqrt{3}}-\sqrt{7-4\sqrt{3}}\\ & =\sqrt{{\left(5+\sqrt{3}\right)}^2}-\sqrt{{\left(2-\sqrt{3}\right)}^2}\\ & =5+\sqrt{3}-2+\sqrt{3}\\ & =3+2\sqrt{3}\\ & =3+2\times 1.73\\ & =3+3.46\\ & =6.5\end{array}$$