The sentence is not grammatically correct, it should be, "Last summer, Jim mowed one lawn, now he mows three." Mowed just one lawn doesn't make sense in one sentence.
B. She is charmed by his attention and wants to please him.
Explanation:
Why does Sylvia consider helping the young man? She is charmed by his attention and wants to please him. She enjoys helping people. It is part of her religion.