13. Sharon drives from her home to her mother's home at a constant speed, taking exactly 180 minutes. One day, she drives at her usual speed until she has covered $\frac{1}{3}$ of the distance, when she encounters a snowstorm. After that, she reduces her speed by 20 miles/hour, and the entire trip takes 276 minutes. The total distance from her home to her mother's home is ( ) miles.
(A) 132
(B) 135
(C) 138
(D) 141
(E) 144
14. Same as the 10th grade, question 19.
13. B.

Let the total distance be $x$. Then Sharon's usual speed is $\frac{x}{180}$. Thus, before encountering the blizzard, she traveled $\frac{x}{3}$ of the distance at this speed, and then, she slowed down by 20 miles/hour, meaning her new speed was $\frac{x}{180}-\frac{1}{3}$ miles/hour.
$$
\text{Therefore, } \frac{\frac{x}{3}}{\frac{x}{180}}+\frac{\frac{2 x}{3}}{\frac{x}{180}-\frac{1}{3}}=276 \Rightarrow x=135 \text{. }
$$