Hey there! :D
We can subtract the two equations.
3n+m=14
n+m=1
3n-n=2n
m-m=0
14-1= 13
We are left with:
2n=13
Divide both sides by 2.
n=6.5
Plug that in to find m.
n+m=1
6.5+m=1
Subtract both sides by 6.5.
m=-5.5
Now, put the values for m and n into the last equation for the value.
n-m
6.5-(-5.5)
Two negatives make a positive.
6.5+5.5= 12
The value is 12.
I hope this helps!
~kaikers