[tex] \left \{ {{2x+3 (x+y)=11,} \atop {7 (x+21y)-6x=-59}} \right. [/tex]

2x+3x+3y=11       5x+3y=11       5*(-59-147y)+3y=11    -295-735y+3y=11
7x+147y-6x=-59   x+147y=-59    x=-59-147y

-295-732y=11
-732y=11+295
-732y=306
y=306:(-732)
y=-51/122

x=-59-147*(-51/122)
x=-59+61 55/122
x=2 55/122