Помогите решить систему уравнений

$\mathtt{\left[\begin{array}{ccc}\mathtt{3x-y=a}\\\mathtt{x-3y=b}\end{array}\right}$ , тогда

$\displaystyle\mathtt{\left\{{{\frac{2}{a}-\frac{5}{b}-\frac{2}{a}-\frac{4}{b}=3-\frac{6}{5}}\atop{\frac{2}{a}+\frac{4}{b}=\frac{6}{5}}}\right\left\{{{\frac{9}{b}=-\frac{9}{5}}\atop{\frac{2}{a}+\frac{4}{b}=\frac{6}{5}}}\right\left\{{{b=-5}\atop{a=\frac{10b}{6b-20}=\frac{-5*5}{-5*3-10}=1}}\right}$

$\displaystyle\mathtt{\left\{{{x-3y=-5}\atop{3x-y=1}}\right\left\{{{3x-9y-3x+y=-15-1}\atop{x=\frac{y+1}{3}}}\right\left\{{{y=2}\atop{x=1}}\right}$