Rate of change is expressed through (Final Amount - Initial Amount) / Time. She has a final amount of $290 and an initial amount of $170 over the time period of 10 weeks (According to the problem). Therefore, you can eliminate choices B and D. Next you simply calculate which equation gives you a greater value in the answer choices. In this case, (290-170)/10 gives you a greater value than (290-190)/10. That being said, the answer is answer choice C.