Question

Resolva
m+n=20
2m+4n=54

Answer 1

m + n = 20
2m + 4n = 54

m = 20 - n

2.(20 - n) + 4n = 54 
40 - 2n + 4n = 54
2n = 54 - 40
n= 14/2
n = 7

m = 20 - n
m = 20 - 7
m = 13

=)