First you want to find how many words she types per hour.
There are 60 minutes in 1 hour.
So multiply 70 words/min times 60 min/ 1 hr to cancel out the minutes.
You will get 4200 words / hr
Then multiply 4200 by 4 and 5
use * as multiplication symbol
4200 words/hr * 4 = 16,800 words/hr
4200 words/hr * 5 = 21,000 words/hr
She will type 16,800 - 21,000 words/hr
So Your answer is going to be letter G