Answer
It is unusual because $P(4~or~more)\lt0.05$
Work Step by Step
The probability to find 4 or more is the complement of the probability to find 3 or fewer.
Using the Complement Rule (see page 275):
$P(4~or~more)=1-P(3~or~fewer)=1-0.9841=0.0159$
$P(4~or~more)\lt0.05$. So, it is an unusual event.
