Open THIS FILE and unhide all faces and vertices.
Choose tool Create\Object\Copy, switch to front view, click on the body (or click
and drag along horizontal [H] axis). The dialog box will appear:
...type another name (body2, for the instance) there and hit ok.
Choose Modify\Mirror tool, select horizontal modify axis ( [H] ) and mirror
the object (if you have clicked while copying the object, but not clicked and dragged you will
see the following image:
As you see, cars' half is has invalid visible side and needs to be reoriented with
Modify\Reorient tool (apply on objects level).
After reorienting you might notice, that the cars' half isn't good-shaded (differs from
original) this happens because normals after mirroring haven't been mirrored. As a rule,
this fault if fixed with reorient tool, by holding CTRL hey down and clicking on the object.
But since we have automatic normals update option switched on, it is sufficient to move
the copied half (to it's position) and normals will be automatically updated:
As you might notice, we have two objects instead one. To merge them you should use
Create\Object\UniteSelect tool (unite selected). It combines (merges/fuses) selected objects
into one object. Thus you have to select these objects and apply this tool, giving an unique
name for "new" object (High body, for the instance).