Answer
a) 146
b) 145
c) 84
Work Step by Step
(a) We know that $U^{238}_{92}$ has the following number of particles.
$Z=92$, $A=238$
Now $N=A-Z=238-92=146$
(b) For $Pu^{239}_{94}$
$Z=94$, $A=239$ and $N=A-Z=239-94=145$
(c) For $Nd^{144}_{60}$
$Z=60$, $A=144$ and $N=A-Z=144-60=84$