But now how can I solve the algebra problem??? Is there a Function for that???
Excel does not really do algebra. If you wanted, you can use the Goal Seek/Solver utilities to "solve" the equation, but the algebra in this case is so simple that I don't know why you would want to bother with that kind of solution (especially if this is headed into VBA).

Here's your algebra lesson for today (http://www.purplemath.com/modules/solvexpo2.htm). Excel has the built in logarithm function =LOG() and =LN(). VBA only has the natural log Log() function.