Walking with 4/5 of my usual speed, I miss the bus by 5 minutes. What is my usual time?	Select the correct option:
A) 145
B) 5617
C) 15
D) 20
E) 12

Rationale: "speed ratio = 1 : 4 / 5 = 5 : 4 time ratio = 4 : 51 - - - - - - - - 5 4 - - - - - - - - - ? è 20 answer : d"
Answer: D