The integer expressed in decimal as $300$ is expressed in hexadecimal as $12 \mathrm C$.
 $\ds 12 \mathrm C_{1 6}$ $=$ $\ds 1 \times 16^2 + 2 \times 16 + 12$ $\ds$ $=$ $\ds 256 + 32 + 12$ $\ds$ $=$ $\ds 300$
$\blacksquare$