It is known that the perimeter of triangle XYZ is 70 meters. The length of XZ is 2 meters longer than the length of XY. The length of YZ is 6 meters less than the length of XZ. If a represents the length of XY, b represents the length of YZ, and c represents the length of XZ, then the system of three-variable linear equations from the relationship between the lengths of the sides of triangle XYZ is _____.