Question 221134
solve by subsititution method 9m+n=77 m-3n=21


9m + n = 77 ------ (i)

m - 3n = 21 ------(ii)


m  =  21 + 3n ----- Solving for m in eq (ii)


9(21 + 3n) + n = 77 ------ Substituting 21 + 3n for m in eq (i)


189 + 27n + n = 77


28n = - 112


n = {{{-112/28}}} = {{{highlight_green(-4)}}}


m - 3(-4) = 21 ----- Substituting - 4 for n in eq (ii)


m + 12  =  21


m  =  21 - 12 = {{{highlight_green(9)}}}