The prime factorization of 640 can be written as 27 × 51 where 2, 5 are prime.
Word problem: Today the temperature dropped 13 °F. After this drop, the temperature was 74 °F. What was the original temperature outside before the drop?
Subtraction problem: x °F - 13 °F = 74 °F
Solve: x - 13 = 74
x - 13(+13) = 74 + 13
x = 87 °F
If you could show a picture of the clocks I could help you
