Let's look at the options first.
Since we know that Bolt runs 21 miles every day, therefore, option B & option D cannot be the correct answer.
Now we are left with the options A & option C.
Lets read the second statement in the question.
“ Running at the rate of 9 miles per hour for n minutes “.
Since the rate is given in miles per hour but n is given in minutes, therefore we have to convert n minutes into hour by dividing by 60.
⇒(n60)hr
Now, when we look at the options A & C, we can clearly mark option C as the answer.