Of the total 6*6 = 36 possible pairs-outcomes (D1,D2), there are 4 + 3 + 2 + 1 = 10 favorable pairs: 9 = 3+6 = 4+5 = 5+4 = 6+3 (4 pairs), 10 = 4+6 = 5+5 = 6+4 (3 pairs), 11 = 5+6 = 6+5 (2 pairs), 12 = 6+6 (1 pair). Therefore, the probability under the question is= = 0.2778 = 27.78%.
Do it on your own by the same way.