Based on your dates you would have concieved around march 31st. Which is in the middle of both sexual encounters. Only thing you can do is get a paternity test.
According to the due date calculator on **********.com, your due date if you conceived 3/15/09 would have been 12/6/09 and for 4/10/09 would have been 1/1/10. I agree w/ the others that the best way to find out would be a paternity test, though.
Im surprised you havent done a paternity test.... I have no idea, its a close call could be either.
what was your original due date? if you calculate from when your child was born you would have conceived between 3/23 and 3/30. However that is just a guess given the little bit of info you gave. Unfortunately since the dates are close no one on here can tell you for sure who fathered your child and the only way to know for sure is a DNA test. I'm sorry you're going through this though and I wish you the best of luck.
I suggest just getting a paternity test. thats the easiest and most definite thing to do. does your husband know you cheated? if not then that would be a problem. that would be your first step... but if he knows then itll be easy. they dont cost that much.
Did you have a period in between the two? When was your last period before finding out you were pregnant? Did you have her early or on time?