Помогите!!!!!!!!!!!!!!!!??????????

1) $2 \sqrt{a} -6 \sqrt{a} =4 \sqrt{a}$
2) $\sqrt{8a} + \sqrt{18a} = \sqrt{4*2a} + \sqrt{9*2a} =2 \sqrt{2a} +3 \sqrt{2a} =5 \sqrt{2a}$
3) $\sqrt{6} ( \sqrt{24} - \sqrt{54} )=\sqrt{6} ( \sqrt{4*6} - \sqrt{9*6} )=\sqrt{6} ( 2\sqrt{6} - 3\sqrt{6} )=- \sqrt{6} * \sqrt{6}=-6$
=-6
4) $3 \sqrt{12} +2 \sqrt{3} -2 \sqrt{27} =3 \sqrt{4*3} +2 \sqrt{3} -2 \sqrt{9*3} =6 \sqrt{3} +2 \sqrt{3} -6 \sqrt{3} =2 \sqrt{3}$

= $2 \sqrt{3}$
вот