Q$\mathrm{.}2.(25$p$)$ In the mixing of concrete both the gravel and thickness of the mortar can possibly influence the hardess of the resulting concrete $2$ level of gravel size $($factor A$)$ and $3$ levels of mortar thickness $($factor B$)$ were examined in a carefully controlled experiment. For each combination of gravel size and mortar thickness $3$ batches of concrete were mixed and tested for hardness with results shown below:

$\backslash$table$[[,$Mortar thickness $($j$),\frac{?}{\text{b}\text{a}\text{r}}(y{)}_{i.}$