Question 212243
You have a linear system here:

1) N is 5 less that 4 times the measure of angle M
2) Supplementary mean that they add to 180 

{{{system( N = 4M-5, N+M=180 ) }}}
{{{system( N -4M = -5, N+M=180 ) }}}

*[invoke linear_substitution "N", "M", 1, -4, -5, 1, 1, 180 ]