Acidity of primary and secondary amines

I was reading a book on organic chemistry by David Klein and I came across this question, but I wasn't able to understand why one amine is more acidic than the other.

• Have you been able to draw the structures of the conjugate bases? – airhuff Jan 18 '17 at 8:19

Have you taken into account that there is a $\ce{-CH3}$ group attached to the top N which has +I effect i.e., electron donating effect?
$\ce{-CH3}$ group will destabilize the negative charge on N formed after the release of proton.