Answer
There is evidence that says that the mean for untrained tasters is 25 ug/L +
Work Step by Step
Mean = $\frac{30+30+42+...+29+19+23}{10}$ = 29.4
z = $\frac{x-u}{o/\sqrt n}$ = $\frac{29.4- 25}{7/\sqrt 10}$ = 1.99
P = P(Z < -1.99) = 0.0233