\left \{ {{\frac{x+1}{3}-\frac{y+2}{4}=\frac{2(x-y)}{5}}(*60) \atop {\frac{x-3}{4}-\frac{y-3}{3}=2y-x}} \right. (*12)
\left \{ {{\frac{60(x+1)}{3}-\frac{60(y+2)}{4}=\frac{60*2(x-y)}{5}}\atop {\frac{12(x-3)}{4}-\frac{12(y-3)}{3}=12(2y-x)}} \right.
\left \{ {{20(x+1)-15(y+2)=24(x-y)}\atop {3(x-3)-4(y-3)=24y-12x}} \right.
\left \{ {{20x+20-15y-30=24x-24y}\atop {3x-9-4y+12=24y-12x}} \right.
\left \{ {{20x-15y-10=24x-24y}\atop {3x-4y+3=24y-12x}} \right.
\left \{ {{20x-24x=-24y+15y+10}\atop {-4y-24y+12x+3x=-3}} \right.
\left \{ {{-4x=-9y+10}\atop {-28y+15x=-3}} \right.
\left \{ {{x=\frac{-9y+10}{-4}}\atop {-28y+15(\frac{-9y+10}{-4})=-3}} \right.
\left \{ {{x=\frac{-9y+10}{-4}}\atop {-28y-3,75(-9y+10)=-3}} \right.
\left \{ {{x=\frac{-9y+10}{-4}}\atop {-28y+33,75y-37,5=-3}} \right.
\left \{ {{x=\frac{-9y+10}{-4}}\atop {5,75y=-3+37,5}} \right.
\left \{ {{x=\frac{-9y+10}{-4}}\atop {5,75y=34,5}} \right.
\left \{ {{x=\frac{-9y+10}{-4}}\atop {y=6}} \right.
\left \{ {{x=\frac{-9*6+10}{-4}}\atop {y=6}} \right.
\left \{ {{x=\frac{-44}{-4}}\atop {y=6}} \right.
\left \{ {{x=11}\atop {y=6}} \right.
spr.
\frac{11+1}{3}-\frac{6+2}{4}=\frac{2(11-6)}{5}
\frac{12}{3}-\frac{8}{4}=\frac{2(5)}{5}
4-2=2
2=2
…
\frac{11-3}{4}-\frac{6-3}{3}=2*6-11
\frac{8}{4}-\frac{3}{3}=1
2-1=1
1=1