Merging rows

Hello,

Client has requested that I merge certain rows of data in this table

CREATE TABLE `answer` (
`id` int(11) NOT NULL auto_increment,
`applicant` varchar(255) REFERENCES applicant(id),
`question` int(11) REFERENCES question(id),
`answer` text NOT NULL,
PRIMARY KEY (`id`)
)

The relationship between each question and applicant is unique.

What I need to do is look up each applicant's answers to question 3
and question 4 and merge them into the answer for question 3.

I was feebly trying things like:

UPDATE testAnswer SET answer = CONCAT(
(SELECT answer AS start
FROM testAnswer WHERE question = 3)
UNION
(SELECT answer AS finish
FROM testAnswer WHERE question = 4)
GROUP BY applicant
)

Can anyone point me in the right direction?

TIA

JG