Step 1: Find the total possible points before the final exam:
Total possible points = 5 tests * 100 points = 500 points
Step 2: Find the total points earned before the final exam:
Total points earned = 75 + 86 + 70 + 61 + 96 = 388 points
Step 3: Let x be the score Brandi needs on the final exam. Since the final exam will count as two tests, the total points earned after the final exam will be:
388 + x
Step 4: The average score with the final exam included will be:
\frac{388+x}{7}=80
Step 5: Solve for x:
388+x=7*80
388+x=560
x=560-388
x=172
Answer: Brandi needs to score 172 on the final exam in order to have an average score of 80.