Walking with 4/5 of my usual speed, I arrive at the bus stop 7 minutes later than normal. How many minutes does it take to walk to the bus stop at my usual speed? Pick one
A) 12  B) 16  C) 20  D) 24  E) 28

Rationale: let t = usual time = distance / usual speed t + 7 = distance / ( 4 * usual speed / 5 ) = ( 5 * distance ) / ( 4 * usual speed ) = 5 t / 4 t = 28 the answer is e .
Answer: E