Question 192834
(x+6)^2=3(x+12)-x^2

x^2+12x+36 =3x+36-x^2

2x^2+9x=0

x(2x+9)=0

x=  0,  (-9/2)    ANSWER

check
x=0

6^2=3*12   

36=36  ok

x=(-9/2)

(-4.5+6)^2=3(-4.5+12)-(-4.5)^2

1.5^2=3*7.5-20.25
2.25=22.5-20.25=2.25  ok