Safety-first and Normal Distribution someone, example, question, 446

dkishore1

Hi
Could someone explain me the reason why in currc Reading 9 page 446
in example 9 question 3 the largest ratio .090625 has negative N(-0.91)?
question in task was:
Q:What is the probability that return on SFr optimal portoilio will be less that the shortfall level?

P(R<3.75) = N(- .90625)?

What is the reasoning here that we use negaitve sign N(-x)?

thanks
R