Traffic signals: The number n of seconds for the yellow light of a traffic signal is a function of the width w, in feet, of the crossing street. a. Explain the meaning of dn dw in practical terms.  b....

Traffic signals: The number n of seconds for the yellow light of a traffic signal is a function of the width w, in feet, of the crossing street.

a. Explain the meaning of dn dw in practical terms.

 b. In certain settings the equation of change for n as a function of w is

and the number n is 4.7 seconds when the width w is 70 feet. Find a formula for n as a function of w.