Eva begins an 8 week program to improve her health. By the end of first week, she can do 10 sit-ups in a row. By the end of the second week, she can do 15 sit-ups in a row. By the end of the third week, she can do 20 sit-ups in a row. If Eva continues at this rate, how many sit-ups can she do in a row by the end of the training program?