I have a Yard King lawn mower model number 46572x89 the longer mower belt part number 710217 was destroyed what size is this belt or where can I purchase one?

Hi,
These are Murray part numbers though they may not look familiar. I also find they have the more familiar #37X66 and #37X89 (second seems to change to #7769211MA) part numbers. Breakdowns can be found at:
Murray lt Parts Diagram Index for 46572X89 (http://partsandservice.com/html/Murray/lt/lt46572x89.html)
and
http://www.oscar-wilson.com/MANUALS/MURRAY/46572X8.PDF
with the second only being the same family of mower and will have different hood, etc.
Peace,
Clarke