Answer:
His humble attitude made it easy for everyone to like him.
Explanation:
As already stated in the question, the word "humble" denotes someone who is not authoritative but rather open and down to earth, approachable.
Supposing it is to be replaced by the synonym "modest", though its's meaning may still be the same, its word usage will be slightly different from that of "humble".
So, the replacement of the word "humble" by "modest" will be best suitable in the last sentence where the attitude of the man is talked about. Due to his "modest" attitude, which makes him easily approachable, it made it easy for people to like him.
