I've looked over the book again and you're right. The formula written in blue ink is for two-tailed test. The only difference is that you divide alpha by 2 if it's a two tailed test while you don't divide alpha by 2 for a one-sided test.

I have two last questions that are bothering me.

1.) Presented below in the image is the formula to calculate -Z_{B}. Is there any modification I need to do if I want Z_{B}? Because that's what I need to plug in the formula.

2.) The formula for n has that weird symbol that looks like an unfinished 8. How do I calculate that?