b)
[tex]\frac{3}{3b-1} = \frac{3,9}{6,5} \ \ \rightarrow \ \ b\neq \frac{1}{3}\\\\\frac{3}{3b-1} = \frac{39}{65}\\\\\frac{3}{3b-1} = \frac{3}{5}\\\\3(3b-1) = 15\\\\9b - 3 = 15\\\\9b = 15+3\\\\9b = 18 \ \ /:9\\\\\underline{b = 2}[/tex]
c)
[tex]\frac{3\frac{3}{4}}{5} = \frac{1}{1+c} \ \ \rightarrow \ \ c\neq -1\\\\\frac{\frac{15}{4}}{5} = \frac{1}{1+c}\\\\\frac{15}{20} = \frac{1}{1+c}\\\\\frac{3}{4} = \frac{1}{1+c}\\\\3(1+c) = 4\\\\3+3c = 4\\\\3c = 4-3\\\\3c = 1 \ \ /:3\\\\\underline{c = \frac{1}{3}}[/tex]
d)
[tex]\frac{1+d}{5-2d} = \frac{1,6}{2,4} \ \ \rightarrow \ \ d \neq 2,5\\\\\frac{1+d}{5-2d} = \frac{16}{24}\\\\\frac{1+d}{5-2d} = \frac{2}{3}\\\\3(1+d) = 2(5-2d)\\\\3+3d = 10 - 4d\\\\3d+4d = 10-3\\\\7d = 7 \ \ /:7\\\\\underline{d = 1}[/tex]
