x2+5x-14=(x+7)(x-2), so the length=x+7, width=x-2. These factors must be positive so x>2cm. The width must exceed 1cm, therefore x-2>1, x>3cm. So, for example, if x=4cm, length=11cm and width=2cm.
Length>10cm, width>1cm. The difference between length and width is always 9cm.