a)a+b=30 => a=30-b
[tex] \frac{a}{b} = \frac{3}{7} \\ a + b = 30 = > a = 30 - b \\ inlocuim \: in \: raport \\ \frac{30 - b}{b} = \frac{3}{7} = > 7(30 - b) = 3b \\ 210 - 7b = 3b \\ 210 = 10b \\ b = 21 \\ \\ a = 30 - 21 = 9[/tex]
[tex] b)\frac{a}{b} = \frac{3}{7} \\ a - b = 12 = > a = 12 + b \\ inlocuim \: in \: raport \\ \frac{12 + b}{b} = \frac{3}{7} = > 7(12 + b) = 3b \\ 84 + 7b = 3b \\ 84 = - 4b \\ 21 = - b \\ b = - 21 \\ \\ a = 12 + ( - 21) \\ a = 12 - 21 \\ a = - 9[/tex]
