4 : 16/19 = 4 * 19/16 = 19/4
3 * 5/12 = 15/12 = 5/4
3 * 13/24 = 39/24 = 13/8
19/4 + 5/4 - 13/8 = 24/4 - 13/8 = 6 - 13/8 = 48/8 - 13/8 = 35/8