The output $X$ of a process depends on the levels of two adjustable variables: $A$, a factor with four levels, and $B$, a factor with two levels. For each combination of a level of $A$ and a level of $B$, nine independent values of $X$ are observed.

Explain and interpret the $R$ commands and (abbreviated) output below. In particular, describe the model being fitted, and describe and comment on the hypothesis tests performed under the summary and anova commands.