1.he is only a child of 11 years old 改为同义句 he is only ———.2.

1.he is only a child of 11 years old. he is only an 11-year-old boy.
因为11eleven是元音开头,所以要用an,这一点很多同学容易乎略
2. he was kind of enough to help me.如是没猜错,肯定是多个了of
he was so kind that he would help me.或he was so kind a man/he was such a kind a man that he would help me.
3. 世界上没有免费的午餐之类的好事 there is no such thing（that is） like a free lunch.
或者 thee is not a thing（that is） like a free lunch.
虽然是谚语,但是翻译起来方法也很难统一.

希望有用