We should be her score in the seventh test to achieve an average of 80

Explanation
To score an average of 80 after the 7th she needs to have 80*7=560 in total, then:
[tex]\begin{gathered} 98+82+79+63+77+80+x=560 \\ 479+x=560 \\ x=560-479 \\ x=81 \end{gathered}[/tex]Answer
81