For this question, a quick way of knowing the answer is by a unit analysis, if we want to obtain inches from feet, then we have to divide by foot and multiply by inches:
[tex]\frac{\text{feet}}{\text{foot}}\times\text{inches.}[/tex]
Now, the above expression is the same as:
[tex]\text{feet}\times\frac{inches}{foot}\text{.}[/tex]
Answer: Last option, we have to multiply by:
[tex]\frac{12\text{ inches}}{1\text{ foot}}.[/tex]
