I'm guessing that an angle of 800 and 500 means 80 degrees and 50 degrees respectively. It doesn't help things when your notation is poor.

Have you drawn a simple diagram? The sine rule is the wrong tool for the job. The cosine rule is what's required:

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Although you should see from your simple diagram that there's another way of doing it using right angle triangles ...... (use this method to confirm your answer).