$14\mathrm{.}6\mathrm{.}4.$ VS An experiment described by M$.$ G$.$ Natrella in the

National Bureau of Standards$$ Handbook of Experimental Statistics $(1963,$ No$.91)$ involves flame$-$testing fabrics after applying

fire$-$retardant treatments. The four factors considered are type of

fabric $($A$),$ type of fire$-$retardant treatment $($B$),$ laundering condition $($C$$the low level is no laundering, the high level is after one

laundering$),$ and method of conducting the flame test $($D$).$ All factors are run at two levels, and the response variable is the inches

of fabric burned on a standard$-$size test sample. The data are: