Firstly convert base 3 into a decimal number system(Base 10):
$(210)_3=(x)_{10}\implies 0*3^0+1*3^1+2*3^2=(21)_{10}$
Now convert $(21)_{10}$ into a hexadecimal system. dividing by $16$ that is:
$(21)_{10}=(z)_{16}$
$\therefore z =(15)_{16}$
Option $A$ is correct.