(A) H₀ is that the treatment has no significant effect, that is, that µ=150.
(B) Ha is µ≠150 (the claim).
(C) Critical Value is 2.5669 for 2-tail t test with a significance level 0.02 and degrees of freedom =18-1=17 (one less than sample size).
(D) Estimated standard error=s/√n=11/√18=2.5927.
(E) Test statistic t=(138-150)/2.5927=-4.6284.
(F) Since t is more extreme than the critical value, H₀ has to be rejected in favour of Ha. It is unlikely (at the significance level specified) that µ=150 after treatment..
(G) The conclusion is that the treatment is significantly effective.