The correct explanation is that James lost a negative sign when combining the x-terms, because -4x + 3x = -x, not 7x.
- Find the like terms in the original expression. The x-terms are -4x and 3x, and the constants are 7 and 2.
- Check the x-terms. The correct sum is -x, but James wrote 7x. He computed instead of , so the negative sign on -4x was lost.
- The constants were combined correctly.
- The only mistake is in the x-terms: James lost the negative sign on -4x. The best explanation is that James lost a negative sign when combining the x-terms.