So at 6 pm was 72, since 6 pm was 8 less degrees than at 4 you would add 8 to 72 degrees to get 80 degrees at 4 pm. Since at 10 it was 5 degrees greater than 4 pm, which was 80 degrees, you would add 5 to 80 and get 85 degrees at 10 am. Your answer is 85 degrees.
