How long to walk ten miles with a 40 pound backpack?

My husband is joining the military. He is trying to train for basic training by walking about 10 miles and carrying a backpack of bricks that we think to weigh right around 40 pounds. He did this and clocked in a two and a half hours the round he is walking on is asphalt city road and partially hilly. i was wondering how long it should take him to walk ten miles with a 40 pound backpack?