Jill typed 84 words in 2 minutes . assuming that she types at a constant rate , how many words does she type in 1 minute , 3 minutes and 9 minutes ?

At the rate of 84 words per 2 minutes, which translates to 42 words per one minute.

So in one minute she types 42*1=42 words
In 3 minutes she types 42*3=126 words
In 9 minutes she types 42*9=378 words

If she typed 84 words in two minutes, and you must find how many words she types at 1 minutes, 3 minutes, and 9 minutes is she was consistent in her speed, all you have to do is find the WPM (words per minute), and then multiply. Since we start with her WPTM (words per two minutes), we simply divide that by two.
84/2=42
So, our WPM rate is 42.
So, she types 42 words in one minute.
42*3=126
She types 126 words in three minutes.
42*9=378
She types 378 words in nine minutes.