6. In a trip, A drives 50 miles on the highway first, then 10 miles on the coastal road. A's speed on the highway is 3 times the speed on the coastal road. If A drives on the coastal road for 30 minutes, then the entire journey took ( ) minutes.
(A) 50
(B) 70
(C) 80
(D) 90
(E) 100
6. C.

From the information that A drove on the coastal road for 30 minutes, we know his speed is $v=\frac{s}{t}=\frac{10}{0.5}=20$ miles/hour. Therefore, his speed on the highway is 60 miles/hour.

Since A drove 50 miles on the highway, he spent 50 minutes on the highway.
Thus, A's entire journey took $30+50=80$ minutes.