Why does Munkres use 3δ instead of δ in exercise 22.12?

[ehrenfest]

[SOLVED] Munkres Exercise 22.12

Homework Statement

Please stop reading unless you have Munkres topology textbook.
Why does Munkres use $$3 \delta$$ instead of $$\delta$$ in part b? I get that replacing the $$3 \delta$$ by $$\delta$$ works fine.

Homework Equations

The Attempt at a Solution

 

[morphism]

\delta does seem to work fine...