The underlined part has two separate errors. "Are replace" is wrong subject-verb agreement with a passive construction, and it should be "are replaced" or "are being replaced". Also "so that to save money" mixes two structures: "so that ... can save" and "in order to save". Only one of these should be used.
Option B is the only version that keeps the passive sense correct and fixes the "so that to" error, so it is the answer.
If the price of a commodity increases by 25%, by what percentage should the consumption be reduced to keep the expenditure the same?