Question 1023813
Subtract eq. 1 from eq. 2,
{{{4x-5y+4z+x+5y+5z=19-2}}}
3.{{{5x+9z=17}}}
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Add eq. 1 to eq. 3,
{{{-x-5y-5z+x+5y-z=2-20}}}
{{{-6z=-18}}}
{{{z=3}}}
Then from eq. 3,
{{{5x+9(3)=17}}}
{{{5x=-10}}}
{{{x=-2}}}
Then from eq. 3,
{{{-2+5y-3=-20}}}
{{{5y=15}}}
{{{y=3}}}