ACT Math Practice Question: Unit conversions with Algebraic Translation

Try this ACT math practice question on factors of a quadratic expression:

The cost of a nylon rope is $p$ dollars per foot. Which of the following expressions gives the cost, in dollars, of $y$ yards and $f$ feet of nylon rope $\textrm{(Note: 1 yard equals 3 feet)}$ ?

1. $\quad p(3y+f)$
2. $\quad p(y+3f)$
3. $\quad p(\dfrac{y}{3} + f)$
4. $\quad p(y+\dfrac{f}{3})$
5. $\quad 3p(y+f)$