a) $$ \sqrt{144} + \frac{1}{\sqrt{0,81}} = 12 + \frac{1}{0,9} = 12 + \frac{10}{9} = \frac{108}{9} + \frac{10}{9} = \frac{118}{9} = 13\frac{1}{9}$$.
$$6 \div 3 = 2$$.
Ответ: $$13\frac{1}{9}; 2$$