What this is, and how can it be put into Sibelius?

Question

If you look at the bass staff, there is one more 16th note than there should be on a 4/4 time signature. Can someone explain this to me? And what is the number of top of the barline?

Answer 1

The three eighth notes (not 16th notes) with the "3" above the beam are a "triplet": three notes in the space of one beat. There are exactly four beats in the measure.

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For instructions on how to enter triplets in Sibelius, see the Sibelius manual entry "Tuplets - how to create".