A student traveled 10 percent of the distance of the trip alone, continued another 30 miles with a friend, and then finished the last half of the trip alone. How many miles long was the trip?  Choose the correct choice from the following:
A) 75 B) 100 C) 125 D) 150 E) 175

Rationale: let x be the total length of the trip . 0.1 x + 30 miles + 0.5 x = x 30 miles = 0.4 x x = 75 miles the answer is a .
Answer: A