What is the amount of expiation for intentionally breaking the fast for three days in Ramadan, while delaying both the make-up fast (qada') and the expiation (kaffarah), knowing that fasting was obligatory and possible?

If you were not an adult (baligh) when you broke your fast, then there is no blame upon you, and no compensatory fasting (qada'), nor expiation (kaffarah).

If you were traveling and by "qasiran" you meant that you were "shortening" (your prayers, i.e., a traveler), then fasting is not obligatory upon you. If you intentionally broke your fast, there is no expiation (kaffarah) upon you, but you must make up the fast (qada') before the next Ramadan.

If you delayed the make-up fast without a valid excuse until the next Ramadan arrived, then along with making up the fast, you owe a compensatory expiation for the delay, which is feeding one poor person for each day. It is not the expiation of feeding sixty poor persons. The required amount to feed is a mudd of food (approximately 750 grams) for each poor person.