Question 746151
Naming the internal angles as a, b, c for the points A, B, and C,
Three equations:   {{{b=32+3a}}}, {{{c=58+a}}}, {{{a+b+c=180}}}.


Putting into a matrix:  rearrange each equation to be in the same type of format as the "180" equation.
System:
{{{a+b+c=180}}}
{{{a-c=-58}}}
{{{3a-b=-32}}}


Do something more to make the system.  You will need the coefficients of the variables to form the matrix.


System:
{{{a+b+c=180}}}
{{{a+0*b-c=-58}}}
{{{3a-b+0*c=-32}}}


This is not yet arranged for rendering on algebra.com site, but your matrix to begin will be like this:
1___  1___  1___  180
1___  0___  -1___  -58
3___  -1___  0___  -32


Can you continue from that?
(I had here a suggestion but am deleting it )
---Okay I see what to try. 
Use R1 to eliminate the column 1 elements into zero in R2 and R3.  Replace R2 with R2-R1.  Replace R3 with R3-3*R1.  Can you decide what to do next? -----