calculate the interest produced by the following three capitals, placed at interest simple, at an annual rate of 4,5%: a) 1st capital: 15000 placed from April 1 to July 15 of the same year; b) 2nd capital: 3500 placed from April 1 to August 25 of the same year; c) 3rd capital: 67560 placed from April 1 to October 2 of the same year