It's simplemente. The rule I showed you before on the other question actually still applies, although it's a bit confusing. The feminine for simple is just simple, so all you have to do is add the "mente".
You want to tell your friends what time it is. select the correct answer. it is 2: 15 a.m. select one: a. son las dos y cuarto de la mañana. c. son las dos y cuarto. d. son las dos y cuatro de la mañana.