Final answer:
When you subtract 2.24 from 1, you end up with -1.24, making option b the correct answer.
Step-by-step explanation:
The student's question asks for the result of the subtraction 1 - 2.24. To solve this, you simply take the number 2.24 away from 1. If you think of this on a number line, starting at 1 and moving 2.24 units to the left, you end up at -1.24.
So, the answer to 1 - 2.24 is -1.24, which corresponds to option b.