Sample Size

I was hoping someone could help guide me to the right equation, if one exists.

I am trying to determin the sample size that would be needed to detect a difference with:
a two sided alpha of 0.05 at 90% power.

The only other information I have is that previous pilot studies indicate probable success rates of 40% and 65% (respectively).

All equations I can find use more details than are made available to me.

Anyone have anymore experience with this?
Thanks for you time.

-:eek: Research Girl!