The angle between two planes is not affected by the constants, because the slopes of the planes are unaffected. The planes can be expressed as vectors. A=(3,-6,2), B=(2,2,-2), where A and B are vectors for the two planes.
A.B (dot product) is 6-12-4=-10. |A| and |B| are the magnitudes of the vectors.
|A||B|=sqrt((3^2+(-6)^2+2^2)(2^2+2^2+(-2)^2)=sqrt(49*12)=sqrt(7^2*2^2*3)=14sqrt(3).
cos(x)=A.B/(|A||B|)=-10/(14sqrt(3))=-0.412393 (approx) is the angle between the normals of the planes, and this angle is also the angle between the planes. So x, the angle between the planes, is cos^-1(-0.412393)=114.36°. The angle is normally expressed as acute, so this angle is 65.64°.