To find out how many pages Brian can read in 3.5 hours, we first need to determine his reading rate in pages per hour.
Brian can read 80 pages in 2 hours, so his reading rate is:
\[ \text{Reading Rate} = \frac{80 \text{ pages}}{2 \text{ hours}} = 40 \text{ pages per hour} \]
Now, to find out how many pages he can read in 3.5 hours, we multiply his reading rate by the number of hours:
\[ \text{Pages in 3.5 hours} = 40 \text{ pages/hour} \times 3.5 \text{ hours} = 140 \text{ pages} \]
Therefore, the answer is:
140 pages.