[tex]\huge\fbox\purple{ANSWER} [/tex]
[tex] \mathsf\pink{v = l \times w \times h}[/tex]
[tex] \mathsf \purple{{72in}^{3} = c \times 4in \times 3in}[/tex]
[tex] \mathsf \pink{ {72in}^{3} = c \times 12 {in}^{2} }[/tex]
[tex] \mathsf \purple{ \frac{72 {in}^{3} }{ {12in}^{2} } = c \times \frac{12 {in}^{2} }{ {12in}^{2} } }[/tex]
[tex] \mathsf \pink{6in = c}[/tex]
[tex] \huge \tt \color{pink}{A}\color{blue}{n}\color{red}{s}\color{green}{w}\color{grey}{e}\color{purple}{r }[/tex]
[tex] \boxed{ \pink✠\underline{ \boxed{ \sf{Volume \: of \: Rectangular \: prism=length × width × height.}}} \pink✠}[/tex]
[tex]\rule{80mm}{2.5pt}[/tex]
[tex] \qquad \sf \: ➛ 72 = c \times 4 \times 3 \\ \qquad \sf \: ➛72 = c \times 12 \\ \qquad \sf \: ➛transporting \: 12 \: in \: divide \\ \qquad \sf \: ➛ \frac{72}{12} = c \\ \qquad \sf \: ➛ \cancel\frac{72}{12} = c \\ \qquad \sf \: ➛6 = c[/tex]
[tex]\rule{80mm}{2.5pt}[/tex]
★ Hence "c" (length) of Rectangular prism (shipping carton) is
[tex]\boxed{ \blue✜\underline{ \boxed{ \sf{length(c)= 6inch \green✓}}} \blue✜}[/tex]
Hope it helps !