Answer
Please see the work below.
Work Step by Step
Lets say X be the product nucleus then the required equation is
$F^{18}_{9}\rightarrow X^{A}_{Z}+e ^{0}_{1}$
We obtain from the subscripts $9=Z+1$ so $Z=8$
Thus the product of the reaction is $X^{18}_{8}$ which shows its oxygen with symbol O.
Hence we obtain the nuclear equation
$F^{18}_{9}\rightarrow O^{18}_{8}+e^{0}_{1}$
