Answer
(a) $n=(t-45)\times4.8$
(b) $76.25° F$
Work Step by Step
(a) For $10°$ increase in Fahrenheit the number of chirps increase by $48$, so $1°$ change corresponds to $4.8$ chirps.
We will have $0$ chirps when: $70-\frac{120}{4.8}=70-25=45°$
We can write the equation:
$n=(t-45)\times4.8$
We can also find it using slope:
$m=\frac{n-n_0}{t-t_0}=\frac{n-120}{t-70}$
Solving this will give us the same equation.
(b) if $n=150$
$150=(t-45)\times4.8$
$t-45=31.25$
$t=76.25°$
