Let X be the result when the below postfix expressionis evaluated:X = 4 5 1 + * 2 / 3 1 2 + * +Let Y be the maximum size of the operand stack, thevalue of X-Y is ________a.21b.23c.15d.17

To solve this problem, we need to evaluate the postfix expression and find the maximum size of the operand stack.

Step 1: Evaluate the postfix expression The postfix expression is evaluated from left to right.

• Push 4 into the stack.
• Push 5 into the stack.
• Push 1 into the stack.
• Pop 1 and 5, perform addition, and push the result (6) into the stack.
• Pop 6 and 4, perform multiplication, and push the result (24) into the stack.
• Push 2 into the stack.
• Pop 2 and 24, perform division, and push the result (12) into the stack.
• Push 3 into the stack.
• Push 1 into the stack.
• Push 2 into the stack.
• Pop 2 and 1, perform addition, and push the result (3) into the stack.
• Pop 3 and 3, perform multiplication, and push the result (9) into the stack.
• Pop 9 and 12, perform addition, and push the result (21) into the stack.

So, X = 21.

Step 2: Find the maximum size of the operand stack The maximum size of the operand stack is reached when we push 1 into the stack before performing the first addition operation. At this point, the stack size is 3.

So, Y = 3.

Step 3: Calculate X - Y X - Y = 21 - 3 = 18.

So, the answer is not in the options. There might be a mistake in the question or the options.