a) $$√196 + 4√0,81 = 14 + 4 \cdot 0,9 = 14 + 3,6 = 17,6$$.
б) $$(3√7)^2 = 3^2 \cdot (√7)^2 = 9 \cdot 7 = 63$$.
в) $$√0,04 \cdot 81 - 7 \sqrt{\frac{1}{49}} = 0,2 \cdot 9 - 7 \cdot \frac{1}{7} = 1,8 - 1 = 0,8$$.
г) $$√7 \cdot √28 = √{7 \cdot 28} = √{7 \cdot 7 \cdot 4} = √{7^2 \cdot 2^2} = 7 \cdot 2 = 14$$.
д) $$\frac{\sqrt{28}}{\sqrt{7}} = \sqrt{\frac{28}{7}} = \sqrt{4} = 2$$.
e) $$√36 = 6$$.
Ответ: a) $$17,6$$, б) $$63$$, в) $$0,8$$, г) $$14$$, д) $$2$$, e) $$6$$