Which of the following algebraic expressions is not simplified?

Option D. a^2+6ab-2ba

Step-by-step explanation:

Option D because we have like terms: 6ab and -2ba=-2ab, then

a^2+6ab-2ba=a^2+6ab-2ab

Simplifying on the right side of the equation adding like terms:

a^2+6ab-2ba=a^2+4ab

x + 107

step-by-step explanation:

let's say that the number he had before the mistake was x. then, he will have 107 dollars more than this, so the answer is x + 107.