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The left hand part in this song is spaced out. This type of left hand stretching is very common in piano music, so this song is good practice for us.
The finger numbers for the right hand at measure 20 are: 1-2-3-1-2-3-4-5. If you don’t know finger numbers, just make sure you play the G with your RH thumb and then the C with your RH thumb as well. You want to end up playing G-E in measure 21 with your thumb and pinky.
In fact, for measure 21-35, you should play the entire right hand part with your thumb and pinky. When you play G-E at measure 21, lock your hand into that “shape” and then move that hand shape up and down the piano.
One more thing, the left hand notes are short during the beginning of the song, but you can add some contrast if you make the left hand smoother starting at measure 37. You don’t have to use the sustain pedal, just hold each note for it’s full value. Then, go back to short left hand notes at measure 51.