I don't understand how to do this problems: Solve for the variable r, C=2PIr (PI is the pi symbol thing then r is next to it) and this problem solve for the variable l, S=B+1/2Pl

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I know this is the same question, but I somewhat understand how to get the answer but I was wondering if someone could break down the steps for me. Because I am working very hard to do well on a test and I need to know the steps for the future. Thanks oh so much! :)

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