Let x be the score he needs to receive on the sixth assignment. If the needs a mean score of 80%, then:

mean score=sun of his scores/number of scores/number

\(\displaystyle{80}\%=\frac{{{82}\%+{74}\%+{66}\%+{83}\%+{75}\%+{x}}}{{6}}\)

\(\displaystyle{80}\%=\frac{{{380}\%+{x}}}{{6}}\)

480%=380%+x

100%=x

He must then score 100% on his sixth assignment to achieve an 80% for the the term.

mean score=sun of his scores/number of scores/number

\(\displaystyle{80}\%=\frac{{{82}\%+{74}\%+{66}\%+{83}\%+{75}\%+{x}}}{{6}}\)

\(\displaystyle{80}\%=\frac{{{380}\%+{x}}}{{6}}\)

480%=380%+x

100%=x

He must then score 100% on his sixth assignment to achieve an 80% for the the term.