The number of pages the student can read in a minute is an illustration of rates.
The time left to complete the whole book is 90 minutes
From the complete question, the student's rate is:

The number of pages is:

First, we calculate the time to read the whole book



The number of the student has read is:

Next, we calculate the time spent on the 25 pages



Convert to minutes

So, the time left is:

This gives


Convert to minutes

Hence, the time left is 90 minutes
Read more about rates at:
brainly.com/question/18065083