The rate is 240 square feet per hour.
EXPLANATION
Firstly, we know that for every 1.5 hours, there is 360 square feet painted. To find how much can be painted in 1 hour, we need to find the half-hourly rate, by dividing 360 by 3, to give us 120 square feet. We then take this away from 360 to give us the hourly rate, which is 240 square feet per hour.
Hope this helps!