Answer :
The volume of a rectangular prism is given by the next formula:
[tex]\begin{gathered} V=l\cdot w\cdot h \\ \\ l=\text{length} \\ w=\text{width} \\ h=\text{height} \end{gathered}[/tex]If you triple the length you get:
[tex]\begin{gathered} V=3l\cdot w\cdot h \\ \\ V=3(l\cdot w\cdot h) \end{gathered}[/tex]Then, if just the length of a rectangular prism is tripled the volume is also tripled