Chapter P, Problem 6CR

Traffic Signal Traffic engineers study how long the yellow light for a traffic signal should

be. For one intersection, the number of seconds $n$ required for a yellow light is related to the

average approach speed $v$, in feet per second, by

$n=1+\frac{v}{30}+\frac{100}{v}$.

If the approach speed is $80$ feet per second (about $55$ miles per hour), how long the yellow light be?