Answer
Yes, see explanations.
Work Step by Step
a. State the hypotheses and identify the claim.
$H_o: \mu=18.3$
$H_a: \mu\ne18.3$ (claim)
b. Find the critical value(s).
$\alpha=0.2, \alpha/2=0.1, |z_c|=2.33$
c. Compute the test value.
$z=\frac{20.9-18.3}{\sqrt {32.49/48}}=3,16$
d. Make the decision.
Since $z\gt z_c$, we reject the null hypothesis and confirm the claim.
e. Summarize the results.
At the 0.02 level of significance, it can be concluded that the mean time
differs from 18.3 hours per week.