Wouldn't

Yes.
Add a comma.

EThanks, Clive. What about this one,
I was happy when he left the job. He wouldn't work in the front. He would only work in the back. 'Would' or 'wouldn't' here has been used to criticise people's behaviour or habits. Are they correct?

Yes

Thanks a lot, once again.

tenjingEach time I gave him a problem he wouldn't solve it for me.

I'm a little uncomfortable with a negative main clause with an "each time" or "every time" clause. If it were my thought to express in English I'd say it as shown below.

He failed to solve every problem I gave him.
Every time I gave him a problem he failed to solve it fo

Thanks, CJ. I used 'wouldn't'in the sentence to show like someone did something continuously in the past.

You mean the use of 'wouldn't' in the following sentences are different, right, I mean with different meaning.
A. Every time I gave him a problem he wouldn't solve it for me. ("past habit would")
B. He wouldn't solve every problem I ever gave him. ("refusal would")
wouldn't is working differently in the sentences, right? With different meaning?

You don't think A involves refusal? I do.

Your use of every time/every problem here does make things a bit unnatural and more complicated.
More natural is
eg He wouldn't solve any of the problems I gave him.
eg He would never solve any of the problems I gave him.

I am more confused now. My last question is can we use 'wouldn't' to talk about things that often didn't happen in the past? Like,
A. Whenever My grandmother came to my house, she would give me chocolates but my grandfather wouldn't give me anything.
Is this sentence with 'wouldn't' correct?

Yes.