No way to blindly calculate the exact # since their hold % is not always exact and can vary by 1-2%.
If you know what the ballpark average market % is you could simply subtract 54.55% (-120) from say 102.5% (roughly accurate for a dime line) which would give you 47.95% (+109).
This would give you a close figure.
market % on a -110/-110 line would be 52.38% + 52.38%=104.76%