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I believe your answer is:
[tex]c=\frac{j}{u}; u\neq 0[/tex]
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Here’s why:
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[tex]\boxed{\text{Solving for 'c'...}}}\\\\j = uc \\------------\\\rightarrow \frac{j=uc}{u}\\\\\rightarrow \frac{j}{u}=c\\\\\rightarrow \boxed{c=\frac{j}{u}}}; u\neq 0[/tex]
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Hope this helps you. I apologize if it’s incorrect.