The correct preposition to use in this sentence is "to". The phrase "find it hard to" is commonly used to express difficulty in doing something.
The sentence becomes:
He found it hard to contain his anger.
The correct preposition is "to".
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?