Answer: B. 
Step-by-step explanation:
let x denotes the number of mile taxi runs.
Given : Taxi A charges $0.20 per mile and an initial fee of $4.
i.e. the expression to show total charge by Taxi A will be :
Taxi B charges $0.40 per mile and an initial fee of $2.
i.e. the expression to show total charge by Taxi B will be :
Now, the inequality that can determine when the cost of Taxi B will be greater than Taxi A will be :-

Hence, B is the correct answer.