a) -3x + 7y = 28 -4x + 3y = 12
7y - 28 = 3x
x = (7y - 28)/3
Substitution
-4(7y - 28)/3 + 3y = 12
-4(7y - 28)/3 = 12 - 3y
-4(7y - 28) = 3(12 - 3y)
-28y + 112 = 36 - 9y
112 - 36 = 28y - 9y
76 = 19y
y = 76/19
y = 4
x = [(7*4) - 28)]/3
x = [28 - 28]/3
x = 0/3
x = 0 Result x = 0, y = 4
b) x + 3y = -7 -7x - 4y = -19
x = -7 - 3y
Substitution
-7(-7 - 3y) - 4y = -19
49 + 21y - 4y = -19
17y = -19 - 49
17y = -68
y = -68/17
y = -4
x = -7 - 3(-4)
x = -7 + 12
x = 4 Result x = 4, y = -4
c) 3x + 2y = 4 6x - 3y = -27
x = (4 - 2y)/3
Substitution
6(4 - 2y)/3 - 3y = -27
6(4 - 2y)/3 = -27 + 3y
6(4 - 2y) = 3(-27 + 3y)
24 - 12y = -81 + 9y
-12y - 9y = -81 - 24
-21y = -105
y = -105/-21
y = 5
x = (4 - 2(5))/3
x = (4 - 10)/3
x = -6/3
x = -2 Result x = -2, y = 5
d) It is not complete
e) -x + 4y = -5 x - 6y = 7
x = 7 + 6y
-(7 + 6y) + 4y = -5
-7 - 6y + 4y = -5
-6y + 4y = -5 + 7
-2y = 2
y = 2/-2
y = -1
x = 7 + 6(-1)
x = 7 - 6
x = 1 Result x = 1, y = -1