(a) To find the least amount spent in the 50s, we need to look for the amounts that have a "5" in the tens place. The only amount that satisfies this condition is 59 dollars. Therefore, the least amount spent in the 50s was $59.
(b) To find the number of couples that spent an amount in the 30s, we need to count the number of amounts that have a "3" in the tens place. There are two such amounts: 35 dollars and 30 dollars. Therefore, two couples spent an amount in the 30s.
(c) To find the greatest amount spent overall, we need to look for the largest number in the given list. The largest number is 50,144,677 dollars. Therefore, the greatest amount spent overall was $50,144,677.