Assuming the HST is the provincial sales tax in BC, PST is the provincial Sales tax in Quebec, and GST is a national Sales tax charged on both provinces, I would get the following calculations:
a) Initial price is $79. Add on the GST of 5% and `79+.05 xx 79=$82.95` Then add on the 12% HST `82.95+.12 xx 82.95=$92.90` The price at Blackcomb is $92.90
b) Initial price is $79. Add on the GST of 5% `79+.05 xx 79=$82.95` Then add on the 9.5% PST `82.95+.095 xx 82.95=$90.83` So the Price at Mont Tremblant is $90.83.
c) The difference is `92.90-90.83=2.07` The difference in prices is $2.07 cheaper in Quebec than in British Columbia.