To convert a measurement from inches to feet, which unit multiplier should be used?

$\frac{12 \text{ in.}}{1 \text{ ft}}$

$\frac{1 \text{ ft}}{12 \text{ in.}}$

$\frac{12 \text{ ft}}{1 \text{ in.}}$

$\frac{1 \text{ in.}}{12 \text{ ft}}$

A student wants to convert 3 feet to inches and writes the expression $3 \text{ ft} \times \frac{1 \text{ ft}}{12 \text{ in.}}$. Why is this setup incorrect?

The wrong numbers are used in the multiplier.

The units will not cancel correctly.

Multiplication should be division.

The starting measurement is wrong.