What is the best way to: Hang upper cabinets without having to hold their full weight.

a). Make a mark where you want the bottom of the cabinets to go. Use a level to draw a straight line across the wall. Place the top edge of a 2x4 even with the line, screw into place. Rest the bottom of the cabinets on the 2x4 while you screw into place. b). Make a mark where you want the bottom of the cabinets to go. Use a piece of paper to draw a straight line across the wall. Place the top edge of a 2x4 even with the line, screw into place. Rest the bottom of the cabinets on the 2x4 while you screw into place.
Answer:
a).