7 1/2 : 2 1/2 * 3 2/3 - 5 1/3 - 5/13* ( 1 1/2)^3
15/2 : 5/2 *11/3 - 5 1/3 - 5/3*(3/2)^3 = 15/2 * 2/5 * 11/3 - 5 1/3 - 5/3 * 27/8 = 11 - 5 1/3 - 45/8 = 10 3/3 - 5 1/3 - 5 5/8 = 5 2/3 - 5 5/8 = 5 16/24 - 5 15/24 = 1/24