All that you need to solve this task is to use basic Z-statistic approach
Start like that [tex]P(X(BAR) \ \textgreater \ 17)[/tex]
Then you have [tex]Z = X(BAR) - 15 / (6.4/sqrt(30))[/tex]
And to complete the task you need to caclulate that with standard table
[tex]P(Z\ \textgreater \ (17-15)/(6.4/sqrt(30))[/tex]
