Add more explanation

To Ziming,

The first line of the solution is quite vague; The first thing we need to do is find a value of "close to" 69 which will be 64.

I think you need to add more explanation about the reason you choose 64. (there are many other numbers close to 69.)

Although you mentioned in the hint, but it would be better to use the term 'linear approximation' instead of tangent line in the solution. (because the question is about the approximation)

It would be great if you add some explanation before $T(64)=...$.

Thanks!

Hi Hyunju,

Sorry I finished them at this very late day... I added some explanation and let me know if it's still unclear.

Goodnight! Ziming