Solve the Decimal Subtraction: 12.3 - 5.4

To solve this problem, we will perform the subtraction of two decimal numbers: $12.3$ and $5.4$.

Here are the steps to follow:

• Align the decimals: Write the numbers $12.3$ and $5.4$ vertically with their decimal points aligned.
• Subtract the numbers digit by digit: Start from the rightmost digit (tenths place).
  $\phantom{x} \, \, 12.3$
  $- \, \, \, 5.4$
  $\rule{1cm}{0.4pt}$
• From the tenths place, $3 - 4$ requires borrowing. Borrow $1$ from the units place of the top number, turning $12.3$ into $12.2$ and making the tenths digit $3+10=13$. Subtract: $13 - 4 = 9$.
• In the units place, $2 - 5$ needs borrowing as well. Borrow from the tens place: change $12$ into $11$ and $2$ becomes $12$. Then subtract: $12 - 5 = 7$.
• Since no borrowing is needed in the tens place, retain $1$ as is.
• Therefore, the final result is $6.9$.

Thus, the result of $12.3 - 5.4$ is $6.9$.