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