How much money would've saved on $85000 mortgage if interest was 6% rather than 8% for 20 years?

Amount owed at 8% for 20 years (compounded yearly)

= 85000*(1.08)^20
= 396181.36

Amount owed at 6% for 20 years
(compounded yearly)
=85000*(1.08)^20
= 272606.52

Figure out the difference.