Final answer:
The rate at which Brian laid bricks is 225 bricks per hour.
Step-by-step explanation:
To calculate the rate at which Brian laid bricks, we need to divide the number of bricks laid by the time taken.
Brian laid 900 bricks in 4 hours, so the rate at which he laid bricks is 900 divided by 4, which is 225 bricks per hour.
This means that Brian laid 225 bricks in one hour.