= Solution
\b[TODO: Attachment C is absent. Check its contents before treating this as a source-complete answer; the computation below uses the printed table, independent observations, a common within-season <variance> model and an explicitly chosen $5\%$ significance level.]
For a one-factor <analysis of variance>, let $n_j,\bar x_j,s_j$ be the four seasonal sizes, means and <standard deviations>. The weighted grand <arithmetic mean> is
$$
N=1430+1569+1639+2248=6886,\qquad \bar x=\frac{\sum_jn_j\bar x_j}{N}=5.06861458.
$$
This agrees with the rounded annual mean $5.07$. The between-season and within-season sums of squares are
$$
SS_B=\sum_jn_j(\bar x_j-\bar x)^2=2670.154583,\qquad SS_W=\sum_j(n_j-1)s_j^2=61829.619600.
$$
There are $4-1=3$ between-season <statistical degrees of freedom>, because the four fitted seasonal means are compared subject to their weighted grand-mean constraint. There are $N-4=6882$ within-season <statistical degrees of freedom>, because one mean was estimated in each group. The total has $N-1=6885$, equal to their sum. Hence
$$
MS_B=890.051528,\quad MS_W=8.98425161,\qquad \boxed{F=99.06797}.
$$
Under $H_0:\mu_W=\mu_{Sp}=\mu_{Su}=\mu_F$, compare with the <F-distribution> on $(3,6882)$ <statistical degrees of freedom>. The $5\%$ critical value is about $2.60620$, with <p-value> approximately $8.9\times10^{-63}$ from the rounded summaries. \b[Reject equality of all four means very strongly under the stated model.] The omnibus <hypothesis test> establishes that at least one mean differs; it does not identify every pairwise difference.
The summer <variance> is substantially lower than the other three, so the exact common-variance <ANOVA> assumptions deserve checking, as does temporal independence. Raw observations would permit diagnostics and a heteroscedastic or time-dependent analysis. As a cross-check on arithmetic, $SS_B+SS_W=64499.774183$ implies annual sample <standard deviation> $3.06074$, matching the table's $3.06$. The numerical significance must not be mistaken for verification of the unobserved Attachment C or of the sampling model.
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