Let us call x the score on Lena's next test, then we have
[tex]\frac{77+68+91+63+68+x}{6}=77[/tex]The above says that the average of six tests should be 77 and we just need to solve for x.
Simplifying the equation above gives
[tex]\frac{367+x}{6}=77[/tex]multiplying both sides by 6 gives
[tex]367+x=462[/tex]Finally, subtracting 367 from both sides gives
[tex]\begin{gathered} x=462-367 \\ \boxed{x=95.} \end{gathered}[/tex]Hence, Lena needs to score 95 in order that her average be 77.