Let:
x6 = Final score
The mean is given by:
[tex]\begin{gathered} \mu=\frac{x1+x2+x3+x4+x5+x6}{6} \\ where\colon \\ \mu=80 \\ x1=81 \\ x2=89 \\ x3=92 \\ x4=85 \\ x5=66 \end{gathered}[/tex]Solve for x6:
[tex]\begin{gathered} 80=\frac{81+89+92+85+66+x6}{6} \\ 80\cdot6=413+x6 \\ 480-413=x6 \\ x6=67 \end{gathered}[/tex]She needs a 67 on the final exam
