Her final exam will be her 6th exam. To determine the her final exam score we can use this equation:
Mean = All scores/6
70 = (58 + 73 + 85 + 83 + 79 + x )/6 ⇒ x stands for the final exam mark
70 = 378 + x /6 ⇒ Multiple both sides by 6 to cancel it out
420 = 378 + x ⇒ Subtract 378 from both sides to isolate x
420 - 378 = x
42 = x
Therefore, she must get at least 42% on her final to maintain a 70% average.