Angelina walked 960 meters from her home to the grocery at a constant speed. She then walked 480 meters to the gym at double the speed. She spent 40 seconds less on her way from the grocery to the gym than on her way from home to the grocery. What was Angelina's speed, in meters per second, from the grocery to the gym?  Choose the correct choice from the following choices:
A) 2  B) 13  C) 24  D) 36  E) 42

Rationale: "let the speed be x . . . so time taken from home to grocery = 960 / x . . the speed to gym = 2 x . . so time taken = 480 / 2 x = 240 / x . . its given 960 / x - 240 / x = 40 . . 720 / x = 40 . . x = 18 m / secs . . so grocery to gym = 2 * 18 = 36 m / s . . . d"
Answer: D