3x+3y=12 ------ eq'1'
2x-4y=14 -------eq'2'
multiplying eq'1' by 4 & eq'2' by 3
we get
12x+12y=48 ------- eq'3'
6x-12y=42 --------eq'4'
adding eq'3' & eq'4' (eliminating 'y')
we get
18x=90
x=90/18
x=5
substituting value of 'x' in eq '1'
3(5)+3y=12
15+3y=12
3y=12-15
3y=-3
y=-3/3
y=-1
hence, solution set is {5,-1}