A hard metric number ends with a zero or a 5. The 3 lowest hard metric numbers are 5, 10 and 15. 5 + 10 + 15 = 30.
12 fl. oz. = 354 mL. Circa 1992, U. S. soft drink makers started putting 355 mL on 12 oz. bottles and cans so Taiwan and China would accept them.
In 1792, Congress based the U. S. dollar on the meter. 100 cents to the dollar. 1000 mils to the dollar. The U. S. was first with a metric currency. The British Pound Sterling was last to go metric in 1970. I was lost when 12 schillings made a pound and 19 1/2 pence made a schilling, or whatever the heck it was.
The 1 and 2 dollar bills are the only bills which are not imprinted with a hard metric number.