Basic Statistics Question

#1
You spend about $4.00 a day on lunch, give or take a $.25.

A) You receive $.75 back from buying lunch when you paid with a $5.00 bill. Should you be worried you were over-charged?

X = 4.25
u = 4
SD = .25

z = 4.25 - 4 / .25
z = 1
theres a 16% chance i was over charged, not that worried.

B) Why might you want to adopt a one-tailed test? Which tail should I choose? What would happen if i choose the wrong tail?

I'm stuck here, please help!