Question 379446
You are assuming that n=0, which is not the case.  What you really need to do is use the n=12-m to substitute into the first equation in place of the n like this:


n=12-m
2m+3n=28


2m+3(     ) = 28
2m+3(12-m)=28


Now, solve for m:

2m + 36-3m = 28
36-m=28
-m=28-36
-m=-8
m=8


Now, substitute m=8 into the n equation:
n=12-m
n=12-8
n=4


Dr. Rapalje