[tex]a=\frac{3+4,2\div \frac{1}{10}}{\left(1\div \frac{3}{10}-2\frac{1}{3}\right)\cdot \frac{3125}{10000}}=\frac{3+4,2\cdot \frac{10}{1}}{\left(\underbrace{1\cdot \frac{10}{3}-\frac{7}{3}}_{=\frac{3}{3}=1}\right)\cdot \frac{5^{5}}{2^{4}\cdot 5^{4}}}=\frac{3+42}{\frac{5}{2^{4}}}=\frac{45\cdot 16}{5}=9\cdot 16= 144[/tex]
[tex]a=\frac{3,6}{100}\cdot b \Rightarrow 3,6\cdot b = 100\cdot 144 \Rightarrow b = 14400 \div 3,6 \Rightarrow b=4000[/tex]