Join side seams on waistbands & press open.
Fold up seam allowance of inner waistband along lower edge & press.
Stitch top edges of front & back waistband, sides & button step on the right side. Then turn to right side & press.
Pin waistband to waist of pants matching notches & sew (use the edge of inner waistband as a guide)..
Fold seam inside the band & press. Sink stitch (stitch in the ditch) from the right side making sure that you catch inner waistband edge in the seam.