$\begin{array}{l} a)\sqrt 4 + 3\\ = 2 + 3 = 5\\ b)B = \sqrt 5 + \sqrt {{{\left( {6 - \sqrt 5 } \right)}^2}} \\ B = \sqrt 5 + 6 - \sqrt 5 = 6\\ c)C = \dfrac{1}{{2 - \sqrt 3 }} - \dfrac{1}{{2 + \sqrt 3 }} + 4\sqrt 3 \\ C = \dfrac{{2 + \sqrt 3 - \left( {2 - \sqrt 3 } \right)}}{{\left( {2 - \sqrt 3 } \right)\left( {2 + \sqrt 3 } \right)}} + 4\sqrt 3 \\ C = \dfrac{{2\sqrt 3 }}{{4 - 3}} + 4\sqrt 3 = 6\sqrt 3 \end{array}$
