The preposition "against" is used when something is in contact with another surface for support.
The correct sentence should be:
"He leaned against the wall for support."
Thus, the correct answer is Option A ("against").
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?