А) - 8/19 * 13/15 - 8/19 * 2/15 = - 8/19 * (13/15 + 2/15) = - 8/19 * 15/15 = - 8/19
б) 24/25 * 37/43 - 24/25 * (37/43 - 15/16) = 24/25 * 37/43 - 24/25 * 37/43 + 24/25 * 15/16 = 37/43 * (24/25 - 24/25) + 24/25 * 15/16 = 0 + 24/25 * 15/16 = 0 + (3*3)/(5*2) = 9/10 = 0,9