(m-2n)^2+(3m-n)(2m+2n)-(2m+n)(2m-n)
=m²-4mn+4n²+6m²+4mn-2n²-4m²+n²
=3m²+3n²
=3(m²+n²)
=3[(m+n)²-2mn]
=3×(16-2)
=3×14
=42