It doesn't look like this equation has an analytic solution, so it will
probably have to be solved numerically. Standard approach:

1) Arrange equation so it is in the form f(x)=0. One way in this case
(1/Do^4)*(T4+T2/Do)-T1+T3=0
2) Choose a value for Do that appears to be near the solution.
3) Numerically solve the equation. The Solver add-in is a utility in
Excel that can do this. If you need help using Solver, let us know.
4) Double check to make sure the solution found by Solver is
reasonable.

In some cases, there can be more than one solution. Choice of initial
guess will determine which solution is found. In cases where multiple
solutions are possible, it will be up to you to determine which is
meaningful.


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MrShorty
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