Answer
$-14^{\circ}C$.
Work Step by Step
The distance traveled is the same, and equals vt.
$$D=v_1t_1=v_2t_2$$
Use the expression for the speed of sound as a function of temperature, on page 329.
$$((331+0.6(31))m/s)(4.80s)= ((331+0.6(T))m/s)(5.20s)$$
Solve for $T=-14^{\circ}C$.
