Question 324886
You could find the inverse of the coefficient matrix or you could use Gaussian elimination. 
I'll use matrix inversion in EXCEL (MINVERSE function).
[A]={{{(matrix(3,3,5,-3,7,3,1,-2,-1,2,1))}}}
[x]={{{(matrix(3,1,x,y,z))}}}
[b]={{{(matrix(3,1,11,11,11))}}}
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Find the inverse of [A].
[A][x]=[b]
[x]=[A]inv[b]
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det([A])={{{77}}}
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[A]inv={{{(1/77)*(matrix(3,3,5,17,-1,-1,12,31,7,-7,14))}}}
{{{(matrix(3,1,x,y,z))=(matrix(3,1,3,6,2))}}}