Correct

回答 vs 答复

/ huídá vs dáfù /
Strokes

Definition

回答 is a Verb, 答复 as a Verb or Noun, which means [answer; reply].

Example

回答 is concrete, while 答复 has the meaning of "putting into effect".
In the two sentences, the meaning is concrete, so 回答 should be used.
1
Lǎoshī
老师
shuō
  
:
zhānglán
张兰
  
,
huí
回答
xiàmiàn
下面
zhège
这个
wèn
问题
  

The teacher said: would you like to answer the following question, Zhang Lan?

2
Duì
对于
kǎojuàn
考卷
shàng
de
wèn
问题
  
,
一一
zuō
le
huí
回答
  

He answered all the questions on the test paper.

答复, the meaning of "putting into effect" is implied,
3
Duì
mín
居民
chū
提出
de
wèn
问题
  
,
ōuzhèng
区政府
shí
及时
zuō
le
答复
  

The block chief made replies to all the requests the residents asked.

4
Qúnzhòng
群众
de
měi
fēng
láixìn
来信
  
,
yǒuguān
有关
dānwèi
单位
dōu
yào
给予
答复
  

The department made a reply to every letter from the public.

5
Qǐng
zuò
bàogào
报告
de
shì
  
,
jīng
已经
yǒu
le
答复
  

He has made a reply to his report.

Sometimes the meaning is vague (both concrete and abstract), 回答 and 答复 are interchangeable.
6
Duì
men
你们
chū
提出
de
yāoqiú
要求
  
,
men
我们
dìng
一定
huì
gěi
chū
mǎn
满意
de
答复
  
(
huí
回答
  
)
  

As for your request, we are likely to give you a satis factory reply.

答复 is also a Noun, which means "a concrete reply document".
7
gāng
shōudào
收到
le
gōng
公司
gěi
de
fèn
答复
wénjiàn
文件
  

He had just received a reply document from the company.