posted by Margaret .
how is the following simplified
3x to the third power plus 5x to the fifth power
I don't know whether you mean
(3x)^3 + (5x)^5, or
3x^3 + 5x^5.
You could write the first version as
27x^3 [1 + (125/27)x^2]
but that would not really be any simpler.