Answer:
Henry has read per minute 3 pages.
Explanation:
Given:
Henry is an avid reader. He devours 90 pages in half-an-hour.
Now, to find pages Henry has read per minute.
Let the number of pages Henry has read per minute be

Number of pages he devours in half-an-hour = 90 pages.
So, as half an hour is 30 minutes.
Thus, number of pages he devours in 30 minutes = 90 pages.
Now, to get the pages he has read per minute:
According to question:

Dividing both sides by 30 we get:

Therefore, Henry has read per minute 3 pages.