Dear Professor Sisley:

  I, Peter Cooper who is one of your students in the evening class, I am writing this letter to offer my sincere apology forto offer my sincere apology for
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to make an apology for
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to beg pardon for not being able to hand in your given assignment on time. I fully appreciate that this is not remotely acceptable to you.

  As a matter of fact, having felthaving felt
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after feeling
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suffering an acute pain in my backacute pain in my back
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lumbago
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a backache a few months ago, I went to see a doctor. There and then, I was shocked to learnwas shocked to learn
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was dismayed to learn
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was saddened to learn that my problem was sciatica. Treatment of this complication got me into enormous difficulty. To manage its medical costs, I had to take a temporary job along with my studies. In spite of the pain I was in, I did my best to do both activities quite satisfactorilyquite satisfactorily
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quite good enough
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adequately well But I regret to inform you that I have been a little behind schedule in your given assignment.

  At the moment, to compensate forto compensate for
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to put to rights
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to recompense the delay in completing my assignment, I would very much like to request a two-week extension on my deadline. If it is kindly granted, I, in return, will certainly meet any other extra demand you would like to make within my assigned piece of work.

  Once again, I regret any inconvenience caused regret something
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feel apologetic about something
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feel remorse about something.

Respectfully,
Peter Cooper
PS. Please find enclosed my incomplete assignment with my compliments.