Question 975550
Where is R?  This variable is not used in the formula.  How do you solve for a variable is does not occur in a formula?  Cannot be done.


Your formula has r.  In general, {{{r<>R}}}; and normally equating the two is bad algebraic practice.


You might want to solve for r.
Where is r?  In the right member of the equation.
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Undo the last thing, read that carefully, the LAST THING done to r.
This would be to use multiplicative inverse of {{{pi*H^2}}}.


{{{V(1/(pi*H^2))=pi*H^2(r-h/3)(1/(pi*H^2))}}}

{{{V/(pi*H^2)=r-h/3}}}

Next, what to undo?  Use additive inverse of {{{-h/3}}};

{{{V/(pi*H^2)+h/3=r-h/3+h/3}}}

{{{highlight(V/(pi*H^2)+h/3=r)}}}