[General] I would need

[suniljain]

I would need your help with this assignment, do you mind staying back for an hour?

Can I use "for" instead of "with"?

 

[bhaisahab]

No, it would not be correct with "for". Also, you should delete "would" and make it two sentences, thus: "I need your help with this assignment. Do you mind staying back for an hour?".

 

[Tarheel]

Perhaps:

Do you mind working late for an hour?

 

[Tarheel]

Or:

Would you mind working late? Maybe for about an hour?

 

[suniljain]

No, it would not be correct with "for". Also, you should delete "would" and make it two sentences, thus: "I need your help with this assignment. Do you mind staying back for an hour?".

I would need your help for this assignment

Why 'for' is not correct?

 

[Matthew Wai]

Because the preposition used after 'help' should be 'with' according to http://www.oxfordlearnersdictionaries.com/definition/english/help_2

 

[tedmc]

I need somebody to help me with (something) my homework.
Can you get help for me(somebody) to do my homework.

 

[Matthew Wai]

Can you get help for me(somebody) to do my homework.

It sounds like asking someone to do the homework on the speaker's behalf.

 

[Rover_KE]

I would need your help for this assignment​.

Why [STRIKE]'for'[/STRIKE] is "for" not correct?

Please note how to ask the question.

 

[Tarheel]

Suniljian, delete "would" from your sentence, and say:

I need your help with this assignment.