Solution: First, decompose the original formula into factors to get the original formula =3(2x-y) 2, and then substitute the known formula for solution.

Original formula =3(4x2-4xy+y2)( 1 min)

=3(2x-y)2(3 points),

∫2x-y-3 = 0，

∴ 2x-y = 3。 (4 points)

∴ Original formula =3(2x-y)2

= 27.(5 points)

,7,