Matthew tells of "a donkey tied, and a colt with her" (21:2). Mark tells of "a young donkey" (Mark 11:2). How do the two tellings fit?

Each tells it in its own words. In Matthew, Jesus said, "you will find a donkey tied, and a colt with her. Untie them and bring them to me" (21:2), and the disciples "brought the donkey and the colt and laid their clothes on them; and he sat on them" (21:7). In Mark, Jesus said, "you will find a young donkey tied, on which no one has sat" (Mark 11:2), and "They brought the young donkey to Jesus and threw their garments on it, and Jesus sat on it" (Mark 11:7). Favor's Mark 11 sets all four Gospels' tellings side by side, in Four tellings of the way in. Matthew says no more about he sat on them (21:7), none of the Gospels explains the difference, and these notes don't either, or say how the tellings fit.