The scores are,
(7.5, 8, 6, 8.5, 7,7.5,7)
Removing the highest (8.5) and the lowest (6), we have
(7.5,8.0,7.0,7.5,7.0)
with a total of 37.
Final score is 77.7
Let the degree of difficulty be x.
According to the rules, the total remaining scores (37) multiplied by the degree of difficulty (x) equals final score (77.7), =>
37x=77.7
solve for x to get
x=77.7/37=2.1
So the degree of difficulty is 2.1