Question 903022
Use Cramer's rule,

{{{A=(matrix(4,4,2,3,1,2,
                 4,1,2,5,
                 1,2,3,1,
                 2,4,2,3))}}}
{{{abs(A)=-29}}}
.
.
{{{A[a]=(matrix(4,4,20,3,1,2,
                 50,1,2,5,
                 10,2,3,1,
                 15,4,2,3))}}}
{{{abs(A[a])=-480}}}
.
.
{{{A[b]=(matrix(4,4,2,20,1,2,
                 4,50,2,5,
                 1,10,3,1,
                 2,15,2,3))}}}
{{{abs(A[b])=75}}}
.
.

{{{A[c]=(matrix(4,4,2,3,20,2,
                 4,1,50,5,
                 1,2,10,1,
                 2,4,15,3))}}}
{{{abs(A[c])=-15}}}
.
.

{{{A[d]=(matrix(4,4,2,3,1,20,
                 4,1,2,50,
                 1,2,3,10,
                 2,4,2,15))}}}
{{{abs(A[d])=85}}}
.
.
{{{a=abs(A[a])/abs(A)=480/29}}}
{{{b=abs(A[a])/abs(A)=-(75/29)}}}
{{{c=abs(A[a])/abs(A)=15/29}}}
{{{d=abs(A[d])/abs(A)=-(85/29)}}}