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Now rotate a copy of that line and place it over the first rectangle done in step 1 as shown in fig A, select both element and apply the Pathfinder -- Divide operation to cut them, ungroup the results and delete the hole. Now copy the new shape (fig. B), place it behind the former one, add an intersecting line in the upper left corner, an intersecting rectangle in that same corner and an ellipse in the bottom right corner. Select all and Divide, delete unnecessary parts so that at the end you get the side shape of the briefcase (step 5).
Duplicate the front side of the briefcase (step 3) and press E (Free Distort tool) like in step 1 to deform it from both bottom corners.
Make a grid with the Rectangular Grid Tool and apply the settings shown in the picture. Rotate it a bit and apply a distortion (Object -- Envelope Distort -- Make with Warp or Alt+Shift+Ctrl+W).
Use the arch distortion so that you get a set of curved lines as you can see in the picture. Finally, convert the grid from line to shapes with the Object -- Expand Appearance command and cut them with the base shape.
Use the same procedure above to make the stripes for the right side of the briefcase. Note that this time we will not use a Warp Distort but a Free Distort because we need to simulate perspective.
Step 8: Build a gradient
Prepare a decorative stripe under the lines of the front side by duplicating and cutting the shape of step 5. Apply a linear fill with whites and light grays as shown in the picture.
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