In my head: oh, look, a multiple of 7. What's 30 cubed? 27 and three zeros, so not far away. What's 27 cubed? Oh, that's it. One of the things that you shoul

In my head: oh, look, a multiple of 7. What's 30 cubed? 27 and three zeros, so not far away. What's 27 cubed? Oh, that's it. One of the things that you should learn is that the problems that humans set for each other usually involve integers or well known numbers.