Ah, but we actually can do it.
The 70.76 is already an average of all scores so far.
70.76 will be 90% of the final grade, 0.0 will be 10%.
This is just a weighted average situation with a 9:1 ratio.
Final Score = [(9)(70.76) + (1)(0)] / 10 = 63.68.
You're still passing, but don't skip any more tests! :-)