Let the representation of a number in base 3 be 210. What is the hexadecimal representation of the number?

To find the hexadecimal representation:

1. Convert the base-3 number to decimal (base 10):

   $$(210)_3 = 2 \times 3^2 + 1 \times 3^1 + 0 \times 3^0 = 2 \times 9 + 1 \times 3 + 0 = 18 + 3 = 21_{10}$$

2. Convert the decimal number to hexadecimal (base 16):

   • Divide $21$ by $16$:

     $$21 = 1 \times 16 + 5$$

   • Quotient $= 1$, Remainder $= 5$.

   • Thus, $(21)_{10} = (15)_{16}$.

Therefore, the hexadecimal representation is 15, which corresponds to option (A).