1. The problem is to perform vertical subtraction for the given pairs of numbers. 2. The subtraction formula is straightforward: subtract the bottom number from the top number digit by digit, borrowing if necessary. 3. Let's solve the first problem (a): $$ \begin{array}{r} 864 \\ -231 \\ \hline \end{array} $$ Subtract units: $4 - 1 = 3$ Subtract tens: $6 - 3 = 3$ Subtract hundreds: $8 - 2 = 6$ So, the result is $633$. 4. For the second problem (b): $$ \begin{array}{r} 9748 \\ -2635 \\ \hline \end{array} $$ Subtract units: $8 - 5 = 3$ Subtract tens: $4 - 3 = 1$ Subtract hundreds: $7 - 6 = 1$ Subtract thousands: $9 - 2 = 7$ Result: $7113$ 5. For the third problem (c): $$ \begin{array}{r} 4693 \\ -2758 \\ \hline \end{array} $$ Subtract units: $3 - 8$ cannot do, borrow 1 from tens (9 becomes 8), units: $13 - 8 = 5$ Subtract tens: $8 - 5 = 3$ Subtract hundreds: $6 - 7$ cannot do, borrow 1 from thousands (4 becomes 3), hundreds: $16 - 7 = 9$ Subtract thousands: $3 - 2 = 1$ Result: $1935$ 6. For the fourth problem (d): $$ \begin{array}{r} 801 \\ -543 \\ \hline \end{array} $$ Subtract units: $1 - 3$ cannot do, borrow 1 from tens (0 becomes -1, so borrow from hundreds: 8 becomes 7, tens becomes 10, then borrow 1 to units: units $11 - 3 = 8$) Subtract tens: $9 - 4 = 5$ Subtract hundreds: $7 - 5 = 2$ Result: $258$ 7. For the fifth problem: $$ \begin{array}{r} 949 \\ -308 \\ \hline \end{array} $$ Subtract units: $9 - 8 = 1$ Subtract tens: $4 - 0 = 4$ Subtract hundreds: $9 - 3 = 6$ Result: $641$ Final answers: a. 633 b. 7113 c. 1935 d. 258 Extra example given: $$ \begin{array}{r} 5489 \\ -925 \\ \hline 4564 \end{array} $$ This confirms the subtraction method.