Final answer:
The error made by Ella is the misplacement of parentheses.
Step-by-step explanation:
Ella made the error of misplacing parentheses. To simplify the expression 3b+4Runner+(−2b−r), we need to distribute the positive and negative signs to each term within the parentheses. This yields 3b + 4Runner - 2b - r. Combining like terms, we get b + 4Runner - r, which is not the same as b + 5t. Therefore, the correct answer is D. Misplacement of parentheses.