3.6×42.3×3.75-12.5×0.423×28
=3.6×42.3×1.25×3-1.25×10×42.3×0.28
=42.3×1.25×（3.6×3-10×0.28）
=42.3×1.25×（10.8-2.8）
=42.3×1.25×8
=42.3×（1.25×8）
=42.3×10
=423
故答案为：423．