You can put this solution on YOUR website! if every question is worth 1 point then a perfect score is 85 which is equal to 100%
to get a 70%, you would need to answer 60 of the questions right.
59 right and you get a score of 59/85 = 69.4%
60 right and you get a score of 60/85 = 70.6%
you cannot get more than 25 wrong or you won't get the 70%.
this assumes that all the questions are worth 1 point each.