= Solution
Test $H_0:\gamma_d=0$ for both nonreference days, against at least one nonzero day <fixed effect>, conditional on chocolate. There are two added <regression coefficients> and $24-6=18$ residual <statistical degrees of freedom>. The <nested-model F-test> statistic is
$$
\boxed{F=\frac{9.750/2}{107.083/18}=\frac{4.875}{5.9491}\simeq0.8195.}
$$
Under $H_0$ and the <normal linear model> assumptions, $F\sim F_{2,18}$. Its 5% upper critical value is $3.555$, so \b[do not reject the absence of day effects]; the <p-value> is approximately $0.456$. Thus the missing row has two <statistical degrees of freedom>, mean square $4.875$, and the <F-test> value above. These observations do not provide evidence that including day improves the chocolate-adjusted mean model. They do not prove that every possible day effect or chocolate–day <interaction term> is absent.
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