(3 1/8 - 2 5/12) * (-1 3/13) = - 34/39
1) 3 1/8 - 2 5/12 = 3 3/24 - 2 10/24 = 2 27/24 - 2 10/24 = 17/24
2) 17/24 * (-1 3/13) = 17/24 * (-16/13) = - (17*2)/(3*13) = - 34/39
