Используем распределительное свойство умножения, получаем:
3_1/4 * 8 = (3+1/4) * 8/1 = 3*8 + 1/4 * 8/1 = 24 + 8/4 = 24+2 = 26
5_1/3 * 6 = (5+1/3) * 6/1 = 5*6 + 1/3 * 6/1 = 30+ 6/3 = 30+2 = 32
4 * 1_1/2 = 4*(1+1/2) = 4*1 + 4/1 * 1/2 = 4 + 4/2 = 4+2 = 6
7 * 1_1/3 = 7*(1+1/3) = 7*1 + 7/1 * 1/3 = 7+7/3 = 7+ 2_1/3 = 9_1/3