One young bullock, one ram, one lamb of the first year, for a burnt offering:

Matthew Henry's Concise Commentary

7:10-89 The princes and great men were most forward in the service of God. Here is an example to those in authority, and of the highest rank; they ought to use their honour and power, their estate and interest, to promote religion and the service of God in the places where they live. Though it was a time of joy and rejoicing, yet still, in the midst of their sacrifices, we find a sin-offering. As, in our best services, we are conscious that there is sin, there should be repentance, even in our most joyful services. In all approaches to God we must by faith look to Christ as the Sin-offering. They brought their offerings each on a day. God's work should not be done confusedly, or in a hurry; take time, and we shall have done the sooner, or, at least, we shall have done the better. If services are to be done for twelve days together, we must not call it a task and a burden. All their offerings were the same; all the tribes of Israel had an equal share in the altar, and an equal interest in the sacrifices offered upon it. He who now spake to Moses, as the Shechinah or Divine Majesty, from between the Cherubim, was the Eternal Word, the second Person in the Trinity; for all God's communion with man is by his Son, by whom he made the world, and rules the church, who is the same yesterday, to-day, and for ever.