how do u solve equations with 2 varibles.?

Question

for example
6x + 12 = 3y
3x + -6 = y
please tell me exactly how u solved this.

Answer 1

6x - 3y = - 12
3x - y = 6

6x - 3y = - 12
-6x + 2y = - 12--------ADD
- y = - 24
y = 24

6x + 12 = 3y
6x + 12 = 72
6x = 60
x =10

x = 10 , y = 24

Answer 2

you can use a simultaneous equation for this one. The are two ways to answer this equation :
1) by substitution
2) by elimination

for this equation you can only use sub and cannot use use elimination because it will give you -y = 0.

6x + 12 =3y ---(1)
3x + (-6) = y ---(2)

substitute (2) into (1)
6x + 12 = 3(3x - 6)
6x + 12 = 9x - 18
18 + 12 = 9x - 6x
30 = 3x
x = 10

then substitute x = 10 into (2)
3x + (-6) = y
3(10) - 6 = y
30 -6 = y
y = 24

Answer 3

Since your second equation stats y = 3x - 6, just replace it in the first one.

6x + 12 = 3y
6x + 12 = 3(3x-6)
6x + 12 = 9x - 18
30 = 3x
x = 10

Then
x = 10
y = 3x - 6
y = 3(10) - 6
y = 30 - 6
y = 24