http://www.tradingtoday.com/black-scholes
pretty simple calcs t4p
RRS @ 3.5c close , 640 days , rfr 5% & vol of 100% gives RRSO @ 1.5c
note 100% vol is less than the 110% used in the AR to value options and less than the 110% verified as the implied vol for 1yr in Bloomberg. If we throw in 110% we get 1.64c
I'm happy with 100% vol as a guide and the differential is spot on IMHO.