A painter can paint 375 square feet in 3 hours. At this rate, how many square feet can he paint is 7 hours?

The painter can paint 375/3 = <<375/3=125>>125 square feet in 1 hour.

So, he can paint 125 x 7 = <<125*7=875>>875 square feet in 7 hours. Answer: \boxed{875}.