To determine how many square feet Ivan can paint in 3 hours, we first need to find out how many half-hour intervals are in 3 hours.
3 hours = 3 * 2 = 6 half-hours.
Since Ivan can paint 25 square feet every half hour, we multiply the number of half-hour intervals by the amount he can paint in each interval:
6 half-hours * 25 square feet/half-hour = 150 square feet.
Therefore, Ivan can paint 150 square feet in 3 hours.