16. Person A drives 15 miles at a speed of 30 miles per hour, then increases the speed to 55 miles per hour. To increase the average speed to 50 miles per hour, he still needs to drive ( ) miles.
(A) 45
(B) 62
(C) 90
(D) 110
(E) 135
16. D.

Let another $x$ miles need to be driven. Then a total of $15+x$ miles will be driven, and the time used will be
$$
\frac{15}{30}+\frac{x}{55}=\frac{1}{2}+\frac{x}{55} \text { (hours). }
$$

Given that the average speed is 50 miles/hour, we have
$$
\frac{15+x}{\frac{1}{2}+\frac{x}{55}}=50 \Rightarrow x=110
$$