text: Guess x1>=x2>=x3>=x4. Work systematically: 13 =\n13 + 0 + 0 + 0 =\n12 + 1 + 0 + 0 =\n11 + 2 + 0 + 0 =\n11 + 1 + 1 + 0 =\n10 + 3 + 0 + 0 =\n10 + 2 + 1 + 0 =\n10 + 1 + 1 + 1 =\n 9  + 4 + 0 + 0 =\nGo on yourself and count the number of possibilities at the and.\nGood luck\n\nTh