1. The problem is to subtract $27.89$ from $31.45$. 2. The subtraction formula is $a - b$, where $a = 31.45$ and $b = 27.89$. 3. Align the decimal points and subtract digit by digit: $$\begin{array}{r} 31.45 \\ -27.89 \\ \hline \end{array}$$ 4. Subtract the hundredths place: $5 - 9$ is not possible without borrowing. 5. Borrow 1 from the tenths place (4 becomes 3), so $15 - 9 = 6$. 6. Subtract the tenths place: $3 - 8$ is not possible without borrowing. 7. Borrow 1 from the units place (1 becomes 0), so $13 - 8 = 5$. 8. Subtract the units place: $0 - 7$ is not possible without borrowing. 9. Borrow 1 from the tens place (3 becomes 2), so $10 - 7 = 3$. 10. Subtract the tens place: $2 - 2 = 0$. So the result is $3.56$. Final answer: $31.45 - 27.89 = 3.56$