As you read through these melodies, notice how many different rhythms are used, but the notes remain the same. When you encounter problems in reading music, it is a good idea to practice pitch reading and rhythm reading separately, as most problems are one or the other and by separating them you can zero in on the exact thing you need to work on without any other complications.
Each time you solve a reading problem, you make it easier to solve the next one you encounter because many note sequences and rhythms occur again and again in music.