n = 3m + 7
n − 2m = 1
solve second equation for n
n - 2m = 1
n = 1 + 2m
now they are both equal to n, so
3m + 7 = 1 + 2m
solve for m
3m + 6 = 2m
6 = -1m
m = -6
plug in
n − 2(-6) = 1
n + 12 = 1
n = -11
check
-11 = 3(-6) + 7
-11 = -18 + 7
-11 = -11
m = -6
n = -11
D