a) ($\sqrt{20}$ - $\sqrt{45}$ + $\sqrt{5}$)$\sqrt{5}$
= (2$\sqrt{5}$ - 3$\sqrt{5}$ + $\sqrt{5}$)$\sqrt{5}$
= $\sqrt{5}$ .$\sqrt{5}$. (2 - 3 + 1)
= 5. 0 = 0
b) $\sqrt{14+6\sqrt{5}}$ + $\sqrt{14-6\sqrt{5}}$
= $\sqrt{5+2.3.\sqrt{5}+9 }$ + $\sqrt{5-2.3.\sqrt{5}+9}$
= $\sqrt({\sqrt{5}+3)}$$^{2}$ + $\sqrt({\sqrt{5}-3)}$$^{2}$
= $\sqrt{5}$ + 3 + 3 -$\sqrt{5}$ = 6
c