'Number' is a read-only property.
You can call:
hFig = figure( 3 ); set( hFig, 'Position', [9 39 900 300], 'Name', 'Velocity');
though beware that the instruction:
figure(3)
will either create a new figure or, if a figure 3 already exists it will simply bring this existing figure into focus and then act upon that.
